ELEMENTARY   BIOLOGY 


PLANT,   ANIMAL,   HUMAN 


THE  MACMILLAN  COMPANY 

NEW  YORK   .    BOSTON  •    CHICAGO 
DALLAS   •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON   •   BOMBAY  •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


ELEMENTARY  BIOLOGY 

PLANT,  ANIMAL,  HUMAN 


BY 

JAMES   EDWARD   PEABODY,  A.M. 
n 

HEAD    OF    THE    DEPARTMENT    OF    BIOLOGY,    MORRIS    HIGH    SCHOOL 
BRONX,    NEW    YORK    CITY,    AUTHOR    OF    "  STUDIES    IN    PHYSI- 
OLOGY "  AND  "LABORATORY  EXERCISES  IN  ANATOMY 

AND    PHYSIOLOGY  " 
AND 

ARTHUR   ELLSWORTH   HUNT,  Pe.B. 

HEAD    OF    THE    DEPARTMENT    OF    BIOLOGY,    MANUAL    TRAINING 
HIGH    SCHOOL,    BROOKLYN,    NEW    YORK    CITY 


"  The  wild  life  of  to-day  is  not  wholly  ours  to  dispose 
of  as  we  please.  It  has  been  given  to  us  in  trust.  We 
must  account  for  it  to  those  who  come  after  us  and 
audit  our  records."  —  HORNADAY. 


fgorfc 
THE   MACMILLAN  COMPANY 

1913 

All  rights  reserved 


BIOLOGY 

P 

G 


COPYRIGHT,  1912, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  February,  1913. 

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3S^S-^ 


J.  S.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


TO 

THE  MEMORY  OF 

MARTHA  FREEMAN  GODDARD 

WHOSE    DEVOTED    INSTRUCTION    IN    BIOLOGY   IS    A    LASTING 

INFLUENCE    FOR    GOOD    IN   THE    LIVES   OF    HUNDREDS 

OF    BOYS     AND    GIRLS    AND     WHOSE     RARE     SKILL 

IN     LEADERSHIP     IS     AN    INSPIRATION    TO 

EVERY    TEACHER    WHO    KNEW    HER 

THIS  BOOK  IS  DEDICATED 

BY   THE    AUTHORS 


PREFACE 

ALL  the  activities  of  a  plant,  of  an  animal,  or  of  man  may 
be  grouped  in  three  classes.  One  class  embraces  the  func- 
tions relating  to  the  life  of  the  individual  organism.  These 
functions  have  to  do  with  the  processes  of  eating,  digest- 
ing, assimilating,  taking  in  of  oxygen,  producing  of  energy, 
and  excreting  of  waste  matters.  These  may  be  called  the 
nutritive  functions,  if  the  term  is  used  in  its  broadest  sense. 
To  the  second  group  of  activities  belong  the  functions  that 
have  to  do  with  the  perpetuation  of  the  animal  or  plant 
species,  and  these  are  known  as  the  reproductive  functions. 
Living  organisms,  whether  plant,  animal,  or  human,  may,  in 
the  third  place,  be  considered  in  their  relations  to  one  another 
and  especially  to  the  general  welfare  of  mankind.  Thus  we 
may  discuss  the  beneficial  or  injurious  effects,  so  far  as  man 
is  concerned,  of  different  kinds  of  insects  or  of  various  types 
of  bacteria ;  we  may  learn  of  the  activities  of  individual  men 
or  of  groups  of  individuals  which  promote  or  retard  the 
advance  of  human  society ;  or  we  might,  if  we  were  to  carry 
the  study  still  farther,  even  seek  to  learn  the  ways  by  which 
the  higher  thoughts  of  mankind,  as  expressed  in  poetry, 
music,  and  religion,  affect  the  development  of  the  human 
race. 

In  the  preparation  of  this  text,  the  authors  have  sought 
to  keep  continually  in  mind  these  three  classes  of  activities, 
and  to  unify  the  study  of  plant,  animal,  and  human  biology 
by  choosing  those  topics  for  laboratory  work  or  text  descrip- 
tion that  have  to  do  in  a  broad  sense  with  one  or  the  other  of 
the  three  great  groups  of  functions  of  living  things  to  which 

vii 


viii  PREFACE 

we  have  just  referred.  In  doing  this,  they  are  conscious 
that  many  subjects  have  been  slighted  or  altogether  omitted 
which  might  well  be  treated  in  a  year's  work  in  either  botany, 
or  zoology,  or  human  physiology. 

Again,  in  the  treatment  of  a  given  subject,  for  example, 
stems,  fishes,  or  circulation,  special  emphasis  might  be  laid 
on  structure,  on  function,  or  on  the  relation  of  the  given  topic 
to  human  life.  Books  both  interesting  and  scientifically 
worth  while  could  be  prepared  along  any  one  of  these  lines, 
or,  if  time  permitted,  all  three  phases  might  be  equally  em- 
phasized. But  when  we  remember  that  less  than  two  hun- 
dred school  periods  will  probably  be  devoted  by  the  average 
student  to  the  study  of  biology,  the  necessity  for  adhering 
pretty  consistently  to  some  one  plan  is  obvious. 

In  the  judgment  of  the  authors  the  kind  of  biology  most 
worth  while  for  the  average  boy  or  girl  of  fourteen  years 
of  age  is  not  one  based  primarily  on  structure.  Young  stu- 
dents are  naturally  more  interested  in  activities  or  func- 
tions than  they  are  in  mere  form  or  structure.  Hence,  if  we 
wish  to  work  with,  rather  than  "  against  the  grain,"  we  must 
put  function  in  the  foreground  of  our  discussion.  Every  boy 
and  girl  knows,  too,  that  both  plants  and  animals  as  well  as 
human  beings  must  have  food  and  drink,  and  that  they  grow 
and  reproduce  their  kind.  It  is  relatively  much  easier, 
therefore,  to  unify  a  course  like  this  along  physiological  lines 
than  on  the  basis  of  morphology,  or  of  homologies  of  structure, 
many  of  which  are  far  too  complicated  to  be  made  clear  to 
young  students. 

If  properly  outlined  and  presented,  there  is  probably  no 

subject  in  the  school  curriculum  that  can  be  made  of  more 

j  service  to  a  growing  youth  than  can  biology.     Biological 

problems  confront  him  at  every  turn,  and  if  he  is  a  normal 

being,  he  will  have  asked  himself  question  after  question 


PEEFACE  ix 

which  an  elementary  knowledge  of  biology  ought  to  help  him 
to  answer.  Some  of  these  questions  may  be  the  following : 
Whence  comes  the  food  and  oxygen  supply  used  by  man? 
Why  are  food  and  oxygen  needed  in  our  bodies?  Why  are 
some  substances  beneficial  to  the  body  and  others  injurious? 
What  is  the  cause  of  disease,  and  how  is  disease  transmitted  ? 
And  if  we  were  to  tabulate  the  biological  questions  that  occur 
spontaneously  to  the  average  pupil  in  the  first  year  in  the 
high  school,  we  should  doubtless  find  that  a  great  proportion 
of  these  questions  had  to  do  with  the  relation  of  the  living 
;world  to  human  life.  Is  it  not  clear,  therefore,  if  we  are  to 
outline  a  course  in  biology  that  will  best  fit  the  interests  of 
the  "  live  material,"  i.e.  the  boy  or  girl  who  is  to  take  the 
course,  that  the  central  idea  or  factor  must  be  man;  that  all 
the  various  functions  considered  must  have  some  relation  to 
human  life ;  and  that  the  course,  to  be  of  practical  importance, 
must  suggest  to  the  youth  better  ways  of  carrying  on  his  own 
life  and  of  helping  to  improve  the  surroundings  in  which  he 
lives? 

In  order,  however,  to  treat  intelligently  such  a  function,  for 
example,  as  respiration  or  digestion,  it  is  of  course  necessary 
to  know  something  of  the  machinery  by  which  each  of  these 
processes  is  carried  on,  and  so  there  must  be  at  least  a  mini- 
mum consideration  of  the  structure  of  plants,  animals,  and 
the  human  body.  In  every  case,  however,  the  authors  have 
called  attention  only  to  those  details  which  seem  to  be  abso- 
lutely essential  for  an  interpretation  of  the  function  under 
consideration.  Whenever  names  in  common  use  are  suffi- 
ciently accurate  for  descriptions,  these  are  chosen  in  prefer- 
ence to  scientific  terms.  Frequently  the  latter  are  neces- 
sarily used,  and  so,  whenever  their  meaning  is  made  clearer 
by  referring  to  their  derivation  from  Latin  or  Greek,  these 
derivations  are  indicated  in  parentheses. 


X  PREFACE 

The  sections  in  coarse  type  contain  the  material  that  seems 
to  the  authors  most  essential  for  any  clear  understanding  of 
the  subject  as  a  whole,  while  in  fine  type  we  have  put  addi- 
tional laboratory  work  and  text  description  which  we  believe 
to  have  an  important  bearing  on  the  various  topics  discussed. 
If  both  coarse  and  fine  print  on  animal,  or  plant,  or  human 
biology  are  used,  sufficient  material  for  a  half-year  course  in 
either  elementary  botany,  zoology,  or  human  physiology  will 
be  provided. 

In  the  judgment  of  the  authors,  plant  biology  should  always 
be  considered  first  and  human  biology  last  in  the  course  for 
the  following  reasons :  (1)  Plants  lend  themselves  far  more 
readily  to  close  observation  and  especially  to  experiments 
than  do  .animals,  and  so  fundamental  processes  which  apply 
to  all  living  things  can  be  demonstrated  scientifically  from 
plant  material.  (2)  Plants  are  the  final  source  of  all  the  food 
supply  of  animals  and  man,  and  if  the  composition  and  manu- 
facture of  the  nutrients  are  taught  early  in  the  course,  a  solid 
foundation  is  laid  for  all  subsequent  study  of  nutrition  in 
animals  and  man.  (3)  The  purpose  of  the  animal  study  is 
largely  that  of  showing  the  adaptations  of  animal  structure 
to  functions  and  the  relations  of  the  animals  studied  to 
human  welfare.  (4)  And  finally,  if  human  biology  comes 
last  in  the  course,  it  may  be  presented  in  such  a  way  as  to 
review,  sum  up,  and  give  real  significance  to  many  of  the 
facts  learned  earlier  in  the  course.  In  fact,  as  the  work 
proceeds,  comparisons  will  constantly  be  made  between 
plants,  animals,  and  man  to  show  that  the  essential  differ- 
ences in  the  three  kinds  of  organisms  consist  not  in  the  dif- 
ferences in  the  functions  which  they  carry  on,  but  in  the 
organs  by  which  the  functions  are  performed. 

So  far  as  the  order  of  individual  topics  under  plant,  ani- 
mal, and  human  biology  is  concerned,  the  instructor  should 


PREFACE  xi 

plan  the  sequence  that  best  fits  the  season.  In  fact,  the  last 
use  that  a  good  teacher  will  make  of  any  laboratory  manual 
or  text-book  is  that  of  following  it  slavishly.  It  is  the  hope 
of  the  authors,  however,  that  the  laboratory  guides  and  the 
text  descriptions  which  follow  may  be  sufficiently  sugges- 
tive to  help  some  teachers  to  work  out  improved  methods 
in  biological  instruction.  In  Appendix  II  will  be  found  a 
suggested  order  of  topics  which  the  authors  have  found 
satisfactory. 

Living  organisms  are  to  a  large  extent  to  be  regarded  as 
chemical  engines  so  constructed  as  to  liberate  different  kinds 
of  energy.  No  one,  of  course,  knows  in  any  ultimate  sense 
how  even  the  simplest  functions  are  performed  by  the  sim- 
plest animals  or  plants.  But  it  is  utterly  useless  to  attempt 
to  teach  biological  functions  without  first  presenting  some  of 
the  elementary  principles  involved  in  physical  and  chemical 
phenomena.  For  this  reason  the  first  chapter  in  Plant 
Biology  is  devoted  to  the  study  of  the  Composition  of  Lifeless 
and  Living  Things.  In  Chapter  III  is  a  brief  discussion  of 
the  structure  of  a  common  plant,  and  since  cells  are  funda- 
mentally alike  in  structure  and  functions  in  all  living  or- 
ganisms, emphasis  is  laid  early  in  the  course  on  the  essential 
characteristics  of  these  cellular  elements  in  plants.  Another 
topic  which  necessarily  recurs  throughout  plant,  animal,  and 
human  biology  is  the  principle  of  osmosis  and  its  applica- 
tions. The  authors  have  inserted  experiments  which  in  their 
experience  have  helped  to  fix  in  mind  this  important  principle 
and  which  demonstrate  the  necessity  of  digestion  in  plants 
and  animals. 

After  this  brief  consideration  of  the  fundamentals  of  plant 
composition,  structure,  and  processes,  Chapters  V,  VI,  and 
VII  are  devoted  to  the  study  of  the  adaptations  of  plants 
for  performing  nutritive  and  reproductive  functions.  In 


Xll  PREFACE 

Chapter  VIII  are  grouped  experiments  and  descriptions 
the  aim  of  which,  is  to  show  various  ways  in  which  plants 
are  propagated.  This  treatment  presents  only  the  briefest 
statement  of  underlying  principles,  since  any  extended  dis- 
cussion of  this  topic  belongs  to  a  course  in  agriculture. 

In  Chapters  IX  (Plants  in  their  Relation  to  Human  Wel- 
fare) and  X  (Plant  Classification)  the  method  of  presentation 
is  strikingly  different  from  that  adopted  in  the  rest  of  the 
book,  particularly  so  in  the  treatment  of  the  spore-bearing 
plants.  The  authors  believe  that  every  pupil  should  be 
taught  something  of  these  simpler  forms  (especially  bacteria), 
and  that  he  should  get  as  many  of  these  facts  as  possible  by 
observation.  But  to  expect  much  laboratory  work  from  young 
students  on  difficult  microscopic  forms  like  many  of  these 
cryptogams,  is,  we  are  confident,  quite  out  of  the  question. 
We  have,  therefore,  frankly  abandoned  the  inductive  method 
of  study  and  have  suggested  that  the  laboratory  work  be 
largely  in  the  nature  of  demonstrations.  It  is,  of  course, 
understood  that  if  these  forms  are  studied,  the  drawings  and 
descriptions  will  be  prepared  from  material  in  the  hands  of 
the  student. 

In  our  judgment  there  are  few  if  any  biological  topics 
which  are  more  important  in  their  practical  bearings  than  is 
that  of  bacteria.  As  commonly  studied  the  disease-pro- 
ducing effects  of  these  organisms  are  emphasized  so  much  that 
boys  and  girls  do  not  appreciate  that  all  the  work  of  the 
higher  plants  depends  ultimately  upon  the  activity  of  these 
low  forms  of  fungi.  In  order  to  bring  out  this  aspect  of  the 
work  of  bacteria  and  for  other  obvious  reasons  the  structure, 
physiology,  and  economic  benefit  of  these  organisms  are  con- 
sidered in  the  chapter  on  the  relation  of  plants  to  human 
welfare,  while  their  pathogenic  effects  are  reserved  for  dis- 
cussion in  human  biology. 


PREFACE  xiii 

The  method  of  presentation  in  "  Animal  Biology  "  is  some- 
what different  from  that  employed  in  "  Plant  Biology,"  for 
the  reason  that  several  widely  different  types  of  animals  are 
studied.  Limitations  of  time  compel  a  rigid  and  somewhat 
narrow  selection  of  groups  for  intensive  study,  and  only  those 
functions  of  each  animal  are  considered  which  have  some 
relation  to  human  biology,  or  which  have  a  broad,  economic 
bearing.  Thus  insects  are  discussed  largely  because  of  their 
injurious  or  beneficial  effects  upon  mankind  ;  birds  and  fishes, 
because  of  their  economic  importance,  and  because  of  the 
great  need  for  their  conservation;  and  one-celled  animals 
because  of  the  light  they  throw  on  cellular  processes.  Certain 
other  somewhat  less  important  topics  are  considered  inci- 
dentally ;  for  example,  protective  resemblance  and  metamor- 
phosis among  insects,  and  the  striking  adaptations  of  structure 
to  function  in  the  bills,  feet,  and  feathers  of  birds. 

The  animals  suggested  for  additional  study,  if  time  per- 
mits, are  representative  mammals,  reptiles,  amphibia,  arthro- 
pods, molluscs,  worms,  and  ccelenterates.  In  many  classes 
there  are  students  who  can  work  faster  than  the  others,  or 
who  are  interested  in  pursuing  further  their  biological  stud- 
ies. Such  students  may  be  directed  in  carrying  on  some  of 
these  studies  either  in  class  or  outside  of  school  hours.  In 
any  case,  students  are  likely  to  acquire  considerable  infor- 
mation by  reading  these  textbook  descriptions  and  studying 
the  illustrations. 

All  the  work  of  the  year  should  lead  up  to  and  culminate 
in  human  biology.  Here,  too,  however,  many  important  top- 
ics must  be  treated  only  superficially,  or  altogether  omitted, 
on  account  of  lack  of  time.  The  authors  believe  that  in 
this,  the  most  important  part  of  the  course,  practical  hygiene 
should  be  taught  as  effectively  as  possible,  and  that  the 
necessity  for  good  food,  pure  air,  varied  exercise,  and  suffi- 


XIV  .  PREFACE 

cient  sleep  should  be  continually  emphasized.  If  boys  and 
girls  can  be  led  to  conform  their  daily  habits  to  the  princi- 
ples of  healthy  living,  the  course  in  biology  will  have  its 
highest  justification. 

In  the  treatment  of  Stimulants  and  Narcotics,  the  authors 
have  tried  to  state  in  simple  language  the  conclusions  of 
experts  regarding  the  effect  of  tobacco  and  alcohol,  and  to 
present  the  strongest  scientific  arguments  against  the  use  of 
these  substances  which  are  so  injurious  to  growing  youths. 

No  study  of  human  biology  should  be  allowed  to  leave  in 
the  mind  of  the  student  the  idea  that  he  is  merely  a  chemical 
engine  adapted  only  for  the  generation  of  a  certain  amount 
of  physical  energy.  The  primary  object  of  all  secondary 
education  should  be  the  development  of  character  and  effi- 
ciency, and  the  true  teacher  ought  to  find  opportunity  again 
and  again  to  touch  the  individual  life  of  the  young  student. 
Especially  should  this  be  true  in  the  study  of  biology. 
Growing  boys  and  girls  ought  to  come  to  feel,  as  they  have 
never  felt,  that  they  have  in  their  keeping  a  most  complex 
and  wonderful  piece  of  living  machinery  which  can  be  easily 
put  out  of  order  or  even  wrecked.  But,  on  the  other  hand, 
they  should  see  that  if  the  bodily  machine  is  well  cared  for, 
it  is  capable  of  splendid  work  which  may  help  to  increase 
the  sum  total  of  human  efficiency  and  happiness. 

In  the  preparation  of  this  book  the  authors  have  received 
a  great  many  suggestions  from  the  teachers  in  their  own 
departments  and  those  of  other  schools.  Our  thanks  are  due 
to  Miss  M.  Helen  Smith  of  the  Manual  Training  High  School, 
Brooklyn,  N.Y.,  for  several  laboratory  outlines  which  formed 
the  basis  of  corresponding  studies  in  the  following  pages. 
The  authors  have  been  especially  fortunate  in  securing  the 
constructive  criticism  of  Dr.  C.  Stuart  Gager,  Director  of 
the  Brooklyn  Botanic  Garden  of  the  Brooklyn  Institute  of 


PREFACE  XV 

Arts  and  Sciences.  He  has  carefully  read  all  of  the  manu- 
script and  the  page  proofs  of  the  "  Plant  Biology." 

We  are  indebted  to  Dr.  H.  J.  Webber,  Professor  E.  O. 
Fippin,  and  others  at  Cornell  University,  for  valuable  ma- 
terial and  illustrations  for  the  chapter  on  Plant  Propagation. 
We  wish,  also,  to  express  our  hearty  appreciation  of  the 
generous  permission  of  Henry  Holt  &  Co.  to  use  some  of  the 
material  published  in  Peabody's  "  Laboratory  Exercises  in 
Anatomy  and  Physiology."  We  are  fortunate,  too,  in  secur- 
ing from  the  New  York  Botanical  Garden  photographs  for 
the  frontispiece,  and  for  several  fine  cuts  in  the  text,  and  from 
Professor  E.  M.  East  of  Harvard  University  the  cut  for  Fig. 
52,  "  Plant  Biology.  "  Miss  Mabelle  Baker,  Miss  Clara  Lang, 
Miss  Margaret  Cutler,  and  Miss  Grace  Gamble,  students  in 
our  first-year  classes,  have  kindly  prepared  for  us  the  figures 
on  which  their  several  names  appear. 

We  have  been  especially  fortunate  also  in  securing  the 
assistance  of  experts  who  have  read  much  of  the  manuscript 
of  the  "  Animal  and  Human  Biology  "  and  many  of  the  proof 
sheets.  Dr.  E.  P.  Felt,  New  York  State  Entomologist,  Mr. 
E.  R.  Root,  author  of  "A.  B.  C.  of  Bee  Culture,"  and 
Professor  Glenn  W.  Herrick  of  Cornell  University,  have  given 
us  valuable  criticism  of  the  chapter  on  Insects.  Dr.  W.  T. 
Hornaday,  Director  of  the  New  York  Zoological  Park,  has 
read  the  chapters  on  Birds  and  Fishes.  To  Mr.  J.  M.  John- 
son, Head  of  Department  of  Biology  of  the  Bushwick  High 
School,  we  are  also  indebted  for  suggestions  relating  to  Birds. 

Much  of  the  manuscript  of  the  chapter  on  Foods  received 
the  careful  criticism  of  the  late  Professor  W.  O.  Atwater. 
Dr.  William  H.  Park,  Director  of  the  Laboratories  of  the 
New  York  City  Board  of  Health,  and  Dr.  Thomas  Spees 
Carrington,  Secretary  of  the  National  Association  for  the 
Study  and  Prevention  of  Tuberculosis,  have  given  invaluable 


xvi  PREFACE 

assistance  in  the  preparation  of  the  chapter  on  microorgan- 
isms. A  considerable  part  of  the  "  Human  Biology  "  was  crit- 
ically read  by  Dr.  F.  C.  Waite  of  the  Western  Reserve  Medical 
School,  by  Mr.  Harold  E.  Foster  of  the  English  Department 
of  the  Morris  High  School,  and  by  the  late  Miss  Martha  F. 
Goddard  of  the  Morris  High  School,  to  whose  memory  these 
volumes  are  dedicated. 

To  Mr.  E.  R.  Sanborn  of  the  New  York  Zoological  Park, 
and  to  Mr.  A.  E.  Rueff  of  the  Brooklyn  Museum,  we  are 
indebted  for  their  skillful  photography.  The  American 
Museum  of  Natural  History,  the  Brooklyn  Museum,  the 
National  Aubudon  Society,  Doubleday,  Page  &  Co.,  Dodd, 
Mead  &  Co.,  Kny-Scheerer  Co.,  Dr.  C.  F.  Hodge  of  Clark 
University,  Dr.  H.  A.  Kelly  of  Johns  Hopkins  Medical 
School,  Mr.  C.  W.  Beebe  of  New  York  Zoological  Park,  and 
others,  have  permitted  us  to  make  use  of  illustrative  material. 

Cost  prices  for  the  items  on  the  list  of  laboratory  appa- 
ratus and  equipment  were  kindly  furnished  us  by  Bausch  & 
Lomb,  Kny-Scheerer,  and  O.  T.  Louis ;  from  these  prices  the 
estimates  on  pp.  173  to  177,  Appendix  I,  were  prepared. 

J.'E.  p. 

A.  E.  H. 

December  31,  1912. 


TABLE   OF  CONTENTS 
PLA^TT   BIOLOGY 

PAGE 

PREFACE .  vii 


II. 

COMPOSITION  OF  LIFELESS  AND  LIVING  THINGS  . 

j. 

5 

I.     Elements,  Compounds,  and  Oxidation         .        . 
II.     Definitions    ........ 

5 
12 

III.     A  Study  of  the  Food  Substances 
IV.     Manufacture  of  the  Food  Substances  by  Plants  . 

13 
22 

III. 

IV. 

THE  GENERAL  STRUCTURE  OF  PLANTS 
OSMOSIS  AND  DIGESTION 

26 
32 

V.     ADAPTATIONS  OF  THE  NUTRITIVE  ORGANS  OF  PLANTS  39 

I.     The  Structure  and  Adaptations  of  Roots     .         .  39 

II.     The  Structure  and  Adaptations  of  Stems     .         .  45 

III.     The  Structure  and  Adaptations  of  Leaves  .         .  52 

VI.     RESPIRATION  AND   THE   PRODUCTION  OF    ENERGY  IN 

PLANTS 64 

VII.     REPRODUCTION  IN  PLANTS 70 

I.     The  Structure  and  Adaptations  of  Flowers         .  70 

II.     The  Structure  and  Adaptations  of  Fruits    .         .  89 

VIII.     PLANT  PROPAGATION 97 

I.     Seeds  and  their  Development  into  Plants    .        .  97 
II.     (Optional.)     Other  Methods  of  Plant  Propaga- 
tion      105 

III.  Conditions  Essential  for  the  Growth  of  Plants  .  108 

IV.  (Optional.)     The  Struggle  for  Existence  and  its 

Effects        .        . 114 

V.     (Optional.)    The  Improvement  of  Plants  by  Man  119 
xvii 


xviii  TABLE    OF   CONTENTS 

CHAPTER  PAGE 

IX.     PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE        .  126 

I.     Some  of  the  Uses  of  Plants  to  Man  ....  126 

II.     The  Uses  of  Forests  and  Forest  Conservation  .         .  132 

III.     Fungi  and  their  Relation  to  Human  Welfare  .         .  139 

X.     PLANT  CLASSIFICATION 154 

I.     (Optional.)     Common  Methods  of  Classification     .  154 

II.     (Optional.)     Scientific  Methods  of  Classification     .  158 


ANIMAL  BIOLOGY 

I.    INSECTS 1 

I.     Butterflies  and  Moths 1 

II.  Grasshoppers  and  their  Relatives     ....  22 

III.  Bees  and  their  Relatives 31 

IV.  Mosquitoes  and  Flies        .         .        .         .                 .43 
V.     (Optional.)     Additional  Topics  on  Insects      .         .  59 

II.    BIRDS 62 

I.     Characteristics  of  Structure 62 

II.     Reproduction  and  Life  History         ....  69 

III.  Methods  of  Classification 73 

IV.  Importance  of  Birds  to  Man 83 

V.     Decrease  in  Bird  Life       .         .        .        .        .         .91 

VI.     Conservation  of  Birds 97 

III.  FROGS    AND    THEIR    RELATIVES 101 

IV.  FISHES 120 

I.     Characteristics  of  Structure 120 

II.     Adaptations  for  Nutritive  Functions     .         .         .  125 

III.  Reproduction  and  Life  History      ....  137 

IV.  Importance  of  Fishes  to  Man         ....  141 
V.     Conservation  of  Food  Fishes .        .         .  147 


TABLE  OF  CONTENTS  XIX 

CHAPTEB  PAGE 

V.    CRAYFISHES  AND  THEIR  RELATIVES 151 

VI.  PARAMECIUM  AND  ITS  RELATIVES 164 

I.  Structure  and  Functions  of  Paramecium       .         .     164 

II.  Structure  and  Functions  of  Amoeba      .        .        .     170 

III.  Cellular  Structure  of  Higher  Animals   .         .        .172 

IV.  Importance  of  Protozoa  to  Man     ....     173 

VII.  (OPTIONAL.)     ADDITIONAL  ANIMAL  STUDIES         .        .     175 

I.     Porifera 175 

II.  Ccelenterata 176 

III.  Annelida 179 

IV.  Mollusca 181 

V.     Reptiles 185 

VI.     Mammals 187 

VII.     Classification  of  Animals  190 


BIOLOGY 

I.     GENERAL  STRUCTURE  OF  THE  HUMAN  BODY         .        .  1 

II.    MICROORGANISMS    AND    THEIR    RELATION   TO    HUMAN 

WELFARE 10 

I.     Structure  and  Functions  of  Bacteria    ...  10 

II.     Occurrence  of  Bacteria 14 

III.  Bacteria  as  the  Friends  of  Man    ....  20 

IV.  Bacteria  as  the  Foes  of  Man         ....  23 

III.      FOODS    AND    THEIR    USES 44 

I.     Food  Substances  found  in  the  Human  Body       .  44 

II.     The  Necessity  for  Foods 45 

III.  The  Composition  of  Foods 46 

IV.  Uses  of  the  Food  Substances        ....  50 
V.     Cooking  of  Foods 52 

VI.     Food  Economy      .......  56 

VII.     Daily  Diet 60 


XX  TABLE  OF  CONTENTS 

CHAPTER  PAGE 

IV.    STIMULANTS  AND  NARCOTICS 64 

I.  Definitions    ........  64 

II.  Beverages      ........  65 

III.  Tobacco 75 

IV.  Drugs  and  Patent  Medicines         ....  78 


V.     DIGESTION  AND  ABSORPTION  OF  THE  NUTRIENTS  .        .       82 

I.     General  Survey  of  the  Digestive  System      .         .       82 

II.    Jfhe  Mouth  Cavity  and  its  Functions  .  84 

III.  (Optional.)     The    Throat   Cavity  and  Gullet 

and  their  Functions       .....       92 

IV.  The  Stomach  and  its  Functions   .         .        .         .93 
V.     The  Small  Intestine  and  its  Functions         .         .97 

VI.     (Optional.)    The  Large  Intestine  and  its  Func- 
tions        98 

VII.     Absorption  from  the  Alimentary  Canal        .         .       98 

VIII.     (Optional.)     The  Liver  and  its  Functions  .         .     101 

IX.     Hygiene  of  Digestion 102 


VI.     CIRCULATION  OF  THE  NUTRIENTS 107 

I.     Composition  of  the  Blood 107 

II.     Circulation  and  its  Organs 108 

III.  The  Heart     .'  .         .         .        .        .         .109 

IV.  The  Blood  Vessels         .        .        .        .        .         .112 

V.  Circulation  of  the  Blood       .         .         .        .         .117 

VI.  Hygiene  of  the  Circulation  .         .         .         .         .119 

VII.     RESPIRATION   AND   THE   PRODUCTION  OF   ENERGY  IN 

MAN          . 122 

I.     Necessity  for  Respiration        ......     122 

II.  Adaptations  for  securing  Oxygen  and  for  excreting 

Carbon  Dioxid 124 

III.  The  Process  of  Breathing      .        .         .         .        .        .129 

IV.  Hygiene  of  the  Respiratory  Organs       ....     132 


TABLE  OF  CONTENTS  xxi 

CHAPTER  PAGE 

VIII.     (OPTIONAL.)    ADDITIONAL  TOPICS  IN  HUMAN  BIOLOGY     139 

I.  The  Skin 139 

II.  The  Skeleton 144 

III.  The  Muscles 150 

IV.  The  Nervous  System 154 

V.  The  Eyes 162 

VI.  The  Ears 166 

IX.     (OPTIONAL.)     GREAT  BIOLOGISTS 168 

APPENDIX      ...........    171 

I.     Laboratory  Equipment 171 

II.  Order  of  Topics .        .178 

III.  Biology  Notebooks        .         .         .        .        .        .        .181 

IV.  Review  Topics  in  Plant  Biology          .        .        .        .188 
V.  Review  Topics  in  Animal  Biology       ....     197 

VI.  Review  Topics  in  Human  Biology       ....     202 

VII.  List  of  Suggested  Books  of  Reference  in  Biology       .     207 


PLANT  BIOLOGY 


View  in  the  Hemlock  Forest,  New  York  Botanical  Garden.  —  (Courtesy 
of  New  York  Botanical  Garden.) 


PLANT  BIOLOGY 

CHAPTER  I 
GENERAL  INTRODUCTION 

1.  Lifeless  Things  and  Living  Things.  —  As  we  look  about 
us,  we  find  that  the  world  in  which  we  live  is  wholly  composed 
of  two  classes  of  things,  which  we  commonly  speak  of  as 
living  things  and  lifeless  things.  Soil,  air,  and  water,  for 
example,  we  know  to  be  lifeless.  Water  is  probably  the 
simplest  of  these  three  so  far  as  its  composition  is  concerned. 
Soil,  on  the  other  hand,  is  very  complex  in  composition,  being 
formed  of  nearly  all  the  substances  known  to  the  scientist. 
Enveloping  the  earth  is  a  mixture  of  gases  called  the  atmos- 
phere which  extends  outward  in  every  direction  for  a  dis- 
tance of  about  fifty  miles.  Everybody  knows,  too,  that  over 
the  surface  of  the  earth,  in  the  water,  and  even  in  the  air 
are  countless  numbers  of  living  things  which  we  designate 
as  either  plants  or  animals. 

One  might  think  that  it  would  be  an  easy  matter  to  set 
down  the  characteristics  by  which  living  things  are  dis- 
tinguished from  those  that  are  lifeless.  And  such  is  the  case 
when  we  compare  a  rock  in  a  field  with  a  horse  that  is  feeding 
beside  it.  Unlike  the  animal,  the  lifeless  rock  is  unable  to 
move  itself,  it  neither  eats  nor  breathes,  and  it  gives  no 
evidence  of  feeling  or  of  will  power.  . 

But  suppose  we  select  for  comparison  a  railroad  locomotive 
and  a  horse.  Both  move ;  both  need  a  plentiful  supply  of  air ; 
B  1 


2  :  PLANT  BIOLOGY 

both  develop  heat  and  power  to  do  work ;  and  both  give  off 
certain  waste  matters.  The  horse,  we  may  say,  requires  food, 
but  so  does  the  engine ;  for  coal  and  water  are  as  necessary 
for  the  development  of  heat  and  power  in  the  engine,  as  food 
and  water  are  for  a  similar  purpose  in  the  horse. 

When  we  try  to  state  characteristics  that  will  distinguish 
all  plants  from  all  lifeless  objects,  we  find  the  task  still  more 
difficult ;  for  most  plants  do  not  move  about  from  place  to 
place,  it  is  difficult  to  realize  that  they  give  off  heat,  and  they 
do  not  give  evidence  that  they  have  conscious  feelings  as 
do  the  common  animals.  In  spite,  however,  of  these  simi- 
larities, we  are  usually  able  to  distinguish  living  from  life- 
less objects  at  least  by  the  three  following  characteristics. 

2.  Growth  of  Living  Things.  —  In  the  first  place  living 
things  use  some  of  the  food  they  eat  for  growth.     No  one  ever 
heard  of  an  engine  or  other  lifeless  object  beginning  as  a  small 
machine,  and  then  slowly  growing  larger  until  it  comes  to 
have  many  times  its  former  weight.1     Yet  this  is  what  hap- 
pens to  all  plants  and  all  animals.     The  average  child,  for 
instance,  at  birth  weighs  seven  to  eight  pounds ;  while  a  man's 
weight  is  over  twenty  times  as  great.     And  if  we  try  to  com- 
pare the  weight  of  an  oak  tree  with  that  of  an  acorn  from 
which  it  started,  the  amount  of  increase  we  find  to  be  enor- 
mous. 

3.  Repair  of  Living  Things.  —  In  the  second  place,  parts 
of  a  locomotive  or  of  any  other  lifeless  machine  by  continual 
use  become  worn  or  broken,  and  the  engine  must  be  sent  to 
the  machine-shop  for  repairs.     Our  bodies,  too,  are  being 
constantly  worn  away ;  for  every  time  we  make  a  motion  of 

*  While  it  is  true  that  icicles  and  other  crystals  apparently  grow, 
this  kind  of  growth  is  brought  about  wholly  by  the  addition  of  mate- 
rial to  the  outer  surface. 


GENERAL    INTRODUCTION  3 

any  sort,  some  of  our  living  muscle  is  used  up ;  every  time 
we  think  or  exert  our  will  power,  some  of  the  living  brain 
substance  is  probably  changed  into  dead  waste  material. 
But  in  contrast  to  lifeless  machines,  our  bodies  are  self-repair- 
ing. The  food  we  eat  not  only  goes  to  increase  the  size  of 
the  body ;  it  also  furnishes  material  to  make  good  the  wear 
and  tear  of  everyday  life.  This  power  of  self-repair  is  like- 
wise present  in  all  animals  and  in  plants  as  well. 

4.  Reproduction  of  Living  Things.  —  A  third   character- 
istic that  distinguishes  living  things  from  those  that  are  life- 
less is  the  fact  that  they  produce  seeds  (in  the  case  of  plants) 
or  eggs  (in  the  case  of  animals),  which  in  turn  come  to  form 
plants  or  animals  like  those  by  which  these  seeds  or  eggs 
were  produced.     No  lifeless  object  can  do  this.     We  shall 
find  in  our  laboratory  study  that,  while  there  are  a  great 
many  different  methods  of  producing  these  new  organisms, 
still  in  their  essential  features  these  various  methods  of  repro- 
duction are  much  the  same  from  the  lowest  plants  to  the 
highest  animals. 

5.  Summary.  —  In  brief,  then,  we  may  say  that  all  liv- 
ing things  have  the  power  of  growth  from  within,  of  self-repair  1 
and  of  the  reproduction  of  their  kind;  but  that  so  far  as  we  know 
lifeless  objects  possess  none  of  these  powers. 

6.  Science  and  its  Subdivisions.  —  Ever  since  the  dawn  of 
history  we  find  that  mankind  has  been  seeking  to  learn  the 
secrets  of  living  and  lifeless  matter.     During  the  past  century 
our  knowledge  has  increased  so  rapidly  that  many  sciences 
have  been  completely  rewritten.     The  discoveries,  for  ex- 
ample, of  the  characteristics  of  radium  and  of  X-rays  have 
revolutionized  much  of  what  was  formerly  believed  as  to  the 
properties  of  lifeless  matter.     In  the  same  way  our  increased 
knowledge  regarding  germs  and  other  microscopic  plants  and 


4  PLANT  BIOLOGY 

animals  has  made  possible  the  scientific  treatment  of  disease, 
and  what  is  more  important,  the  prevention  of  disease.  As 
our  knowledge  of  the  living  and  lifeless  world  has  increased, 
it  has  become  necessary  to  divide  this  knowledge  into  a  great 
many  different  branches,  some  of  which  are  physics,  chemis- 
try, geology  (a  study  of  the  earth),  mathematics,  psychology 
(a  study  of  mind),  and  biology. 

7.  Biology  (from  Greek,  bi'os  =  life  +  lo'gos  =  discourse)  is 
the  general  name  given  to  the  study  of  all  living  things. 
Hence,  this  science  treats  of  both  animals  and  plants.  If  we 
confine  our  study  to  the  structure  and  activities  of  plants 
alone,  we  call  this  part  of  the  science  plant  biology,  or  botany. 
Animal  biology,  or  zoology,  on  the  other  hand,  treats  of  ani- 
mals. So-called  human  physiology  (better  known  as  human 
biology)  discusses  man,  the  highest  type  of  the  animal  king- 
dom ;  hence,  it  is  a  branch  of  the  science  of  zoology,  which  in 
turn  is  one  of  the  subdivisions  of  the  study  of  biology. 


CHAPTER  II 
COMPOSITION   OF  LIFELESS   AND  LIVING  THINGS 

8.  Introduction.  —  For  a  great  many  years  scientists 
have  been  studying  plants  and  animals,  and  from  this 
study  they  have  learned  that  the  bodies  of  all  living  organ- 
isms, including  human  beings,  are  made  from  substances 
found  in  the  water,  soil,  and  air,  and  that  when  plants  and 
animals  cease  to  live,  their  bodies  are  changed  into  the 
chemical  substances  of  which  soil,  air,  and  water  are  com- 
posed. We  are  now  to  learn  by  experiments  the  charac- 
teristics of  some  of  these  materials  found  in  lifeless  things, 
and  some  of  the  combinations  of  these  materials  in  plants 
and  animals. 

V   I.   ELEMENTS,  COMPOUNDS,  AND  OXIDATION 

Materials:  Splinters  of  wood  and  pieces  of  carbon;  starch, 
sugar,  egg,  meat;  potassium  chlorate,  oxid  of  manganese, pieces  of 
marble,  zinc,  hydrochloric  acid,  lime  water  (see  below) ;  elements  for 
demonstration  (e.g.  phosphorus,  sulphur,  iron,  magnesium) ;  com- 
pounds for  demonstration  (e.g.  magnesium  sulphate,  sodium  nitrate, 
potassium  nitrate,  calcium  phosphate,  calcium  carbonate);  test 
tubes,  thistle  tube,  apparatus  stand,  tray  for  collecting  gases,  de- 
livery tube,  cylindrical  graduate  or  glass  jar.  (All  of  the  materials 
named  above  will  be  found  in  the  chemical  or  physical  laboratory 
of  almost  every  high  school.) 

Preparation  of  lime  water :  Put  into  a  large  bottle  a  good  handful 
of  lime  (freshly  slaked  in  water,  if  possible ;  air-slaked  lime  may  be 
used,  however).  Fill  the  bottle  with  water,  shake  the  mixture,  and 

5 


6  PLANT  BIOLOGY 

allow  it  to  stand  until  needed.  Then  pour  some  of  the  liquid  through 
a  funnel  in  which  is  a  filter  paper.  Collect  the  filtered  lime  water 
in  a  bottle,  and  keep  it  stoppered.  As  soon  as  it  becomes  cloudy, 
throw  it  away  and  obtain  some  more  clear  liquid  by  filtration  as  di- 
rected above.  The  large  bottle  can  be  kept  indefinitely  as  a  stock 
solution  if  it  is  kept  filled  with  water.. 

9.  Carbon  (symbol,  C). — Laboratory  Study  No.  1.     Sug- 
gested as  home  work. 

1.  Prepare  some  charcoal  by  lighting  a  long  splinter  of  wood 

or  a  match  and  then  blowing  out  the  flame.  (Pre- 
pared charcoal  may  be  used.)  Charcoal  is  nearly 
pure  carbon. 

a.  Tell  what  you  have  done. 

b.  Is  carbon  (charcoal)  a  solid,  a  liquid,  or  a  gas  ?    What 

is  its  color  ? 

c.  Of  what  substance  does  this  experiment  prove  that 

wood  is  partly  composed  ? 

2.  Hold  the  tip  of  the  carbon  (charcoal)  in  a  hot  flame. 

a.  State  what  was  done. 

b.  Does  any  of  the  carbon  disappear? 

c.  Will  carbon  burn  ?     How  do  you  know  ? 

3.  State  three  characteristics  of  carbon  (charcoal)  that  you 

have  learned  from  these  experiments. 

4.  Hold  your  hand  over  the  glowing  charcoal  with  your  eyes 

closed.  How  can  you  still  tell  that  the  carbon  is 
burning  ? 

10.  Oxygen    (symbol,    O).  - — Laboratory    Study    No.    2. 
Demonstration. 

Preparation  of  oxygen:  Thoroughly  mix  a  teaspoonful  of  po- 
tassium chlorate  with  about  one-fourth  as  much  black  oxid  of  man- 
ganese. Put  the  mixture  in  a  large  test  tube.  Close  the  mouth  of 
the  test  tube  with  a  stopper  through  which  passes  a  delivery  tube, 
the  other  end  of  which  runs  beneath  the  surface  of  water  in  a  tray. 
Support  the  test  tube  in  a  slanting  position  on  an  apparatus  stand, 
and  heat  the  mixture  gently  with  a  gas  or  an  alcohol  flame,  until 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      1 

the  oxygen  begins  to  be  given  off.  Fill  three  or  four  bottles  with 
water,  cover  each  with  a  piece  of  glass  or  cardboard,  and  invert  the 
first  one  over  the  mouth  of  the  delivery  tube,  removing  the  cover 
when  the  mouth  is  under  water.  Continue  to  heat  the  mixture 
until  the  bottle  is  full  of  oxygen,  then  cover  it  under  water  with  the 
glass  plate  or  cardboard,  and  stand  it  right  side  up  on  the  table. 
In  the  same  way  fill  as  many  jars  as  are  needed  for  the  experiments 
with  oxygen.  (Fig.  1.) 


FIG.  1.  —  Preparation  of  oxygen. 

Prepare  several  bottles  of  oxygen  as  directed  and  allow  them  to 
stand  until  all  fumes  have  settled,  before  answering  the  following 
questions. 

1.  Examine  a  bottle  of  oxygen, 
a.   State  what  you  have  done. 

6.   Do  you  find  oxygen  to  be  a  solid,  a  liquid,  or  a  gas  ? 
c.    State  whether  or  not  oxygen  has  color. 

2.  Heat  some  charcoal  (carbon)  till  it  glows  and  thrust  it 

into  a  bottle  of  oxygen. 

a.  Tell  what  was  done  and  describe  what  happens. 

b.  Does  carbon  burn  better  in  air  (which  is  a  mixture  of 

oxygen  and  other  gases)  or  in  pure  oxygen  ? 

3.  State  the  three  characteristics  of  oxygen  which  you  have 

learned. 

11.  Carbon  dioxid  (formula,  CO2).  —  Laboratory  Study 
No.  3.  Demonstration. 


8 


PLANT  BIOLOGY 


\ 

0 

0 

0 

0 

0 

0 

0 

0 

0 

\ 

t 

g 

/ 

Preparation   of  carbon   dioxid:    Into   a   flask   put  some  pieces 
of  marble,  and  insert   a   stopper  through  which  passes   a  thistle 

tube  and  a  delivery  tube  like  that 
used  in  the  preparation  of  oxygen. 
Pour  into  the  thistle  tube  diluted 
hydrochloric  acid   until   the   lower 
end  of  this  tube  is  covered.     Col- 
lect a  bottle  of  carbon  dioxid  in 
.the  same  way  that  oxygen  is  col- 
lected, keeping  the  mouth  of  the 
bottle  closed  with  a  glass  plate  or 
cardboard.      (Fig.   2.)      Prepare   a 
\  \\       fl^     /      Bottle  of  carbon  dioxid  as  directed, 
\  x^y      /       and  allow  it  to  stand  till  all  fumes 
FIG.  2. -Preparation  of  carbon   have  disappeared,  before  answering 
dioxid  or  of  hydrogen.  the  following  questions. 

1.  Examine  a  bottle  of  carbon  dioxid  and  state  whether  it 

-  is   a  solid,  a  liquid,  or   a  gas.     Compare  this  gas 
and  oxygen  as  to  color. 

2.  Light  a  splinter  of  wood  and  thrust  it  into  the  bottle  of 

carbon  dioxid. 
a.   Tell  what  was  done  and  describe  the  effect  of  the  carbon 

dioxid  upon  the  burning  splinter. 
6.    How  was  the  burning  splinter  or  carbon  affected  by 

oxygen? 

3.  Generate  some  carbon  dioxid  as  suggested  above  and  pass 

it  through  the  delivery  tube  into  a  test  tube  of 
clear  lime  water.  Tell  what  was  done  and  describe 
the  effect  of  carbon  dioxid  on  lime  water.  (Carbon 
dioxid  is  the  only  gas  that  affects  lime  water  in  this 
way ;  hence  the  latter  is  a  reliable  test  for  carbon 
dioxid.) 

4.  State  the  four  characteristics  of  carbon  dioxid  which  you 

have  learned  from  these  experiments. 

5.  Place  in  a  bottle  of  pure  oxygen  a  piece  of  glowing 

carbon,  and  allow  it  to  burn  as  long  as  it  will. 
When  the  carbon  ceases  to  burn,  quickly  remove 


COMPOSITION  OF  LIFELESS  AND   LIVING   THINGS      9 

it,  and  pour  in  some  clear  lime  water,  cork  the 
bottle,  and  shake. 

a.  Tell  what  was  done  and  describe  the  change  that  takes 

place  in  the  lime  water. 

b.  What   substance   is   evidently  formed  when   carbon 

burns  in  oxygen? 

6.  When  carbon  is   burned   in  oxygen,  the   two  unite   to 

form  a  new  substance  entirely  different  from 
either  carbon  or  oxygen.  This  new  substance  is 
called  carbon  dioxid,  because  it  is  composed  of  one 
part  of  carbon  and  two  of  oxgyen. 

a.  Describe  the  composition  of  carbon  dioxid. 

b.  State  the  method  by  which  carbon  dioxid  was  pro- 

duced in  this  experiment. 

7.  (Optional.)     By  means  of  a  glass  tube  blow  the  breath  from  the 

lungs  into  a  test  tube  of  lime  water, 
a.  What  change  do  you  notice  in  the  lime  water  ? 
6.  What  do  you  therefore  conclude  to  be  contained  in  the  breath 

from  the  lungs  ? 

12.    Hydrogen  (symbol,  H)  and  water  (formula,  H2O).  - 
Laboratory  Study  No.  4.     Demonstration. 

Preparation  of  hydrogen  (see  Caution  below) :  Into  a  flask  put 
some  pieces  of  zinc.  (See  Fig.  2.)  Insert  a  stopper  with  two  holes. 
Through  one  of  the  holes  pass  the  lower  end  of  a  thistle  tube  until 
it  nearly  touches  the  bottom  of  the  test  tube,  and  through  the  other 
run  a  short  piece  of  glass  tubing.  To  the  upper  end  of  the  latter 
attach  by  means  of  a  piece  of  rubber  tubing  a  delivery  tube  that  will 
reach  beneath  the  surface  of  a  tray  of  water  such  as  that  used  in 
collecting  oxygen  and  in  the  preparation  of  carbon  dioxid.  Pour 
through  the  thistle  tube  enough  diluted  hydrochloric  acid  to  cover 
the  lower  end  of  the  thistle  tube.  (If  hydrogen  does  not  come  off 
rapidly  enough,  put  into  the  flask  a  bit  of  copper  sulphate.)  After 
the  hydrogen  has  been  given  off  for  several  minutes,  collect  a  bottle 
over  water  in  the  same  manner  as  in  the  oxygen  experiment.  Re- 
move the  bottle,  holding  it  upside  down,  and  place  it  on  the  desk 
hi  this  position.  Allow  the  bottle  to  stand  till  fumes  disappear. 


10  PLANT  BIOLOGY 

Caution :  If  in  3  below  an  explosion  occurs,  collect  another  bottle 
of  hydrogen  before  answering  the  questions,  for  an  explosion  indi- 
cates that  oxygen  is  mixed  with  the  hydrogen,  and  such  a  mixture 
is  dangerous  to  experiment  with. 

1.  Examine  a  bottle  of  hydrogen,  and  state  whether  hydrogen 

is  a  solid,  a  liquid,  or  a  gas.     Compare  its  color  with 
that  of  oxygen  and  carbon  dioxid. 

2.  Thrust  a  lighted  stick  up  into  the  mouth  of  an  inverted 

bottle  of  hydrogen.     (This  experiment  will  be  more 
satisfactory  if  the  room  is  darkened.) 

a.  State  what  was  done  and  tell  how  the  hydrogen  af- 

fected the  burning  stick. 

b.  How  does  the  burning  stick  affect  the  hydrogen  ? 

c.  What  is  one  difference  between  oxygen  and  hydrogen  ? 

d.  What  is  one  difference  between  hydrogen  and  carbon 

dioxid  ? 

3.  If  hydrogen  is  not  being  given  off  from  the  delivery  tube 

in  sufficient  quantity,  pour  into  the  thistle  tube 
some  hydrochloric  acid.  Detach  the  delivery  tube 
from  the  rubber  tube  of  the  hydrogen  apparatus 
and  insert  in  its  place  a  piece  of  glass  tubing,  the 
upper  end  of  which  is  drawn  out  to  a  small  diameter. 
Collect  some  of  the  gas  in  a  test  tube  by  displacement 
of  air  and  light  it.  When  it  burns  with  only  a  slight 
puff,  apply  a  lighted  match  to  the  hydrogen  escap- 
ing from  the  drawn-out  tube. 
Hold  over  the  flame  a  bottle  which  is  clean  and  dry. 

a.  Describe  the  preparation  of  this  experiment. 

b.  What  do  you  find  on  the  inside  of  the  glass? 

c.  What,  therefore,  is  formed  when  hydrogen  burns? 

4.  When  hydrogen  burns,  it  unites  with  the  oxygen  of  the 

air  and  forms  oxid  of  hydrogen,  more  commonly 
known  as  water  (formula,  H2O). 

a.  In  what  respect  does  hydrogen  differ  from  oxid  of 

hydrogen  (water)  in  its  most  common  form? 

b.  State  how  oxid  of  hydrogen  was  formed. 

c.  In  what  respects  is  the  method  of  producing  oxid  of 

hydrogen  (water)  the  same  as  that  of  producing 
oxide  of  carbon  (carbon  dioxid)  ?     (See  11,  5  above.) 

5.  Name  five  characteristics  of  hydrogen. 


COMPOSITION   OF  LIFELESS  AND  LIVING   THINGS     11 

13.  Nitrogen  (symbol,  N)  and  the  composition  of  the  air. 
—  Laboratory  Study  No.  5.  Demonstration. 

Fasten  a  candle  to  a  piece  of  cardboard  and  float  the  latter  on  a 
tray  of  lime  water.  Light  the  candle,  and  cover  the  flame  with 
an  inverted  wide-mouthed  bottle,  bringing  the  latter  slowly  down 
until  the  edge  rests  on  the  bottom  of  the  tray.  Allow  the  candle 
to  burn  as  long  as  it  will.  Then  turn  the  bottle  right  side  up,  cover- 
ing the  mouth  with  the  cardboard,  keeping  inside  the  bottle  the  lime 
wrater  that  has  risen  to  take  the  place  of  the  oxygen.  Shake  the 
contents  of  the  bottle,  to  make  the  lime  water  absorb  the  carbon 
dioxid,  and  allow  it  to  stand  till  the  upper  part  of  the  jar  is  clear. 
Keep  the  bottle  covered  to  prevent  the  mixing  of  air  with  the 
nitrogen. 

1.  Examine  a  bottle  of  nitrogen.     Is  it  a  solid,  a  liquid,  or  a 

gas?     What  is  its  color? 

2.  Thrust  a  burning  splinter  of  wood  into  the  nitrogen. 

a.  Tell  what  was  done.     Does  the  wood   continue  to 

burn? 

b.  Does  the  nitrogen  burn? 

c.  In  what  respect  does  nitrogen  differ  from  oxygen? 

3.  State  four  characteristics  of  nitrogen. 

4.  Why  does  carbon  burn  faster  in  oxygen  than  in  air? 

5.  Air  consists  principally  of  oxygen  and  nitrogen.     The 

water  in  the  bottle  represents  the  amount  of  oxygen 
there  was  in  the  bottle  of  air,  and  the  nitrogen 
occupies  the  rest  of  the  space. 

a.  About  what  fractional  part  of  the  air  in  the  bottle  was 
oxygen  ? 

6.  What  fractional  part  of  the  air  in  the  bottle  is  nitro- 
gen ? 

6.  Expose  to  the  air  of  the  room  for  a  half  hour  or  more  a 

dish  with  some  clear  lime  water. 

a.  Describe  the  experiment,  stating  the  effect  on  the  lime 

water. 

b.  What  substance  does  this  experiment  prove  to  be 

present  in  air? 


12  PLANT  BIOLOGY 

II.   DEFINITIONS 

14.  A  chemical  element  is  a  substance  that  has   never 
been  separated  into  two  or  more  different  kinds  of  matter.1  — 
Over  seventy  of  these  elements  are  known  at  the  present  time, 
and  of  these  seventy,  twelve  are  found  constantly  in  the  liv- 
ing substance  of  plants  and  animals.     The  most  common  of 
these  twelve  elements  are  carbon    (symbol,  C),   hydrogen 
(H),  oxygen  (O),  nitrogen  (N),  su]phur  (S),  phosphorus  (P), 
iron  (Fe),  and  calcium  (Ca),  which  is  found  in  lime. 

[In  addition  to  the  elements  already  studied  (C,  0,  H,  N), 
the  others  mentioned  should  be  shown  to  students;  and  if 
time  permits,  some  of  these  elements  may  be  burned  or  oxi- 
dized in  oxygen  and  the  characteristics  of  the  oxids  thereby 
formed  may  be  discussed.] 

15.  A  chemical  compound  is  a  substance  formed  by  the 
union  of  two  or  more  chemical  elements.  —  Two  of  the  im- 
portant compounds  considered  in  biology  are  carbon  dioxid 
(formula  C02),  which  means  that  it  is  composed  of  one  part 
of  carbon  and  two  parts  of  oxygen,  and  water  (formula  H20), 
which  means  that  it  is  composed  of  two  parts  of  hydrogen  and 
one  part  of  oxygen. 

16.  A  mixture  differs  from  a  compound  in  the  fact  that 
the  elements  or  compounds  of  which  the  former  is  composed 
are  not  chemically  united.  —  In  air,  for  instance,  the  oxygen 
and  nitrogen  are  not  chemically  combined,  but  are  simply 
put  together  as  one  might  mix  pepper  and  salt.     Again,  when 
sugar  is  dissolved  or  mixed  with  water,  the  two  compounds 
are  mingled  so  closely  that  the  sugar  disappears;    it  may 
easily  be  obtained  unchanged  in  its  composition  by  evaporat- 
ing the  water. 

1  There  are,  however,  exceptions  to  this  statement,  but  they  are 
too  technical  for  discussion  in  an  elementary  text-book. 


COMPOSITION   OF  LIFELESS  AND  LIVING   THINGS      13 

17.  Oxidation  is  the  chemical  union  of  oxygen  with  some 
other  substance.  —  It  may  take  place  slowly,  as  when  carbon 
is  made  to  glow  in  the  air ;   or  it  may  take  place  rapidly,  as 
when  carbon  burns  in  oxygen.     But  whenever  oxidation  takes 
place,  (1)  an  oxid  is  formed,  (2)  a  certain  amount  of  heat  is 
produced,  and  (3)  if  the  process  is  sufficiently  rapid,  a  flame 
is  seen. 

III.     A  STUDY  OF  THE  FOOD  SUBSTANCES 

18.  Introduction.  —  The  food  substances  needed  by  plants 
and   animals   may   be   divided   into   five   classes,   namely: 
(1)  carbohydrates  (i.e.  starches  and  sugars) ;   (2)  fats  and  oils; 
(3)  proteins,1  which  are  also  known  as  albuminous  or  nitrog- 
enous substances    (e.g.,  white  of  egg,  lean  meat,  gluten  of 
wheat) ;  (4)  minerals  (e.g.  common  salt,  saltpeter,  phosphate 
of  lime) ;   (5)  water. 

19.  To  determine  the  chemical  composition  of  starch.  — 
Laboratory  Study  No.  6.     Suggested  as  home  work. 

Warm  some  starch  in  an  old  cooking  spoon  in  order  to 
drive  off  any  water  that  may  be  in  it,  but  do  not  allow  it 
to  burn.  To  determine  when  the  starch  is  free  from  water, 
hold  the  heated  starch  under  a  dry,  cold  tumbler,  and  if  no 
moisture  collects  upon  the  tumbler,  the  starch  contains  no 
water.  Now  set  the  starch  on  fire,  and  hold  a  cold,  dry 
glass  over  the  burning  starch. 

1.  Tell  what  you  have  done  and  state  what  is  formed  on  the 

inside  of  the  tumbler  by  the  burning  of  the  starch. 

2.  What  is  the  only  chemical  element  that  could  possibly 

form  water  by  burning  (i.e.  by  uniting  with  oxygen)  ? 

3.  What  chemical  element,  therefore,  must  have  been  pres- 

ent in  the  starch  in  order  to  have  produced  water  when 
dry  starch  is  burned? 

1  The  term  protein  is  used  throughout  this  book  instead  of  proteid, 
because  of  the  unanimous  recommendation  in  favor  of  the  former 
term  by  the  American  Society  of  Biological  Chemists  and  the 
American  Physiological  Society.  See  Science,  April  3,  1908. 


14  PLANT  BIOLOGY 

4.  What  substance  is  left  in  the  cooking  spoon  after  the 

flame  goes  out? 

5.  Name  two  chemical  elements  present  in  starch. 

6.  Starch  also  contains  oxygen.     Name  now  the  three  chem- 

ical elements  of  which  this  nutrient  is  composed. 

20.    To    determine   the    chemical    composition   of    sugar, 
fat,  and  protein.  —  Laboratory  Study  No.  7.     (Optional.) 

1 .  Test  sugar  in  the  same  way  as   directed  in  Laboratory  Study 
No.  6,  1-5  (above). 

a.  Describe  each  of  the  experiments,  giving  results   and    con- 

clusions. 

b.  Sugar,  like  starch,  has  oxygen  also  in  its  composition.     Name 

now  all   the  chemical  elements  of   which  sugar  is  com- 


2.  In  a  similar  way  test  a  fat  (e.g.  lard,  or  the  fat  of  meat). 

a.  State  what  you  do,  what  you  see,  and  what  you  conclude. 
6.  Fat,  like  starch  and  sugar,  has  oxygen  in  its  composition,  but 

in   a   different   proportion.      State,   therefore,  the    three 

elements  present  in  fat. 

3.  (Demonstration.)      Secure    a  vegetable    protein    (e.g.  gluten) 

and  test  it  as  directed  above. 

a.  Describe  your  experiments  and  give  your  results  and  con- 
clusions. 

6.  Besides  the  two  elements  you  have  shown  to  be  present, 
protein  also  contains  oxygen,  nitrogen,  sulphur,  phos- 
phorus, and  often  other  elements.  State,  now,  the 
chemical  elements  of  which  this  food  substance  is  com- 
posed. 

21.  Summary.  —  The  carbohydrates,  as  we  have  learned 
and  as  their  name  implies,  are  composed  of  the  chemical  ele- 
ments carbon,  hydrogen,  and  oxygen.  The  same  three  chemi- 
cal elements  are  likewise  present  in  fats  and  proteins,  but  in 
different  proportions.  Proteins,  however,  in  addition  to  the 
carbon,  hydrogen,  and  oxygen,  contain  at  least  three  other 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     15 

chemical  elements,  namely,  nitrogen,  sulphur,  and  phos- 
phorus; in  fact,  proteins  are  the  most  complex  of  all  chemical 
substances  known. 

Following  is  the  composition  of  the  various  nutrients  stud- 
ied thus  far :  — 

Starch,  composed  of  C,  H,  O  (in  the  proportion 

Sugar,  composed  of  C,  H,  O.    (Grape  sugar  = 

Fat,  composed  of  C,  H,  O. 

Protein,  composed  of  C,  H,  O,  N,  S,  P  (and  sometimes  of 
other  elements). 

22.  Tests    for    the    food    substances.  —  Having    demon- 
strated that  the  various  food  substances  are  chemical  com- 
pounds, each  composed  of  several  chemical  elements,  we  are 
now  to  carry  on  experiments  by  which  it  will  be  possible  to 
test  for  each  of  these  food  substances.     By  this  means  we 
shall  be  able  to  prove  the  presence  or  absence  of  starch,  grape 
sugar,  protein,  fat,  mineral  matters,  and  water  in  the  foods 
used  by  plants,  animals,  and  man. 

23.  To  test  foods  for  starch.     Laboratory  Study  No.  8. 

Materials:  Corn  starch,  grape  sugar,  white  of  egg,  fat  or  oil, 
salt,  water;  various  foods  in  the  home  kitchen;  iodine  solution 
(see  below) ;  test  tubes;  gas  burner  or  alcohol  lamp. 

Preparation  of  iodine  solution:  A  quart  (1000  cc.)  of  iodine  solu- 
tion is  made  by  dissolving  in  5  teaspoonfuls  (40  cc.)  of  water,  one- 
half  teaspoonful  (4  grams)  of  potassium  iodide,  and  one-fourth 
this  amount  of  iodine  (1  gram).  This  solution,  when  thoroughly 
mixed,  should  be  diluted  to  make  one  quart  (1000  cc.).  In  a  clean 
bottle  this  mixture  will  keep  indefinitely.1 

1.  Put  a  small  amount  (size  of  a  pinhead)  of  corn  starch 
in  a  test  tube,  add  water,  shake  the  mixture,  and  boil 
it  over  a  gas  flame.  Pour  into  the  starch  mixture 

1  From  Peabody's  "  Laboratory  Exercises."    Henry  Holt  &  Co. 


16  PLANT  BIOLOGY 

thus  formed  a  few  drops  of  iodine.  What  color  is 
produced  ? 

2.  Try  the  effect  of  iodine  on  each  of  the  other  food  sub- 

stances as  follows :  Put  a  small  amount  of  grape  sugar 
into  a  test  tube;  into  a  second  tube  put  some  white 
of  egg  (protein) ;  into  a  third  some  fat  or  oil ;  into  a 
fourth  some  mineral  matter  (salt) ;  and  into  a  fifth  some 
water.  Add  a  little  water  to  each  and  boil  as  in  1 
above  to  cook  each  nutrient.  Add  a  drop  or  two  of 
iodine  solution  to  each  test  tube. 

Do  any  of  the  colors  thus  produced  resemble  at  all  the 
color  resulting  from  the  addition  of  iodine  to  starch  ? 

3.  From  the  preceding,  state  how  you  can  determine  whether 

or  not  a  substance  contains  starch. 

4.  (Optional  home  work.)     Test  as  many  foods  as  you  can  (e.g. 

oatmeal,  flour,  raw  meat,  milk,  parsnip,  potato,  onions,  ap- 
ples, beans,  rice,  pepper)  in  the  following  way :  Put  a  small 
amount  of  a  given  food  into  a  test  tube  or  in  a  sauce  pan,  add 
a  little  water,  and  boil  to  cook  each  food,  then  add  a  few 
drops  of  iodine.  Before  making  each  test  make  sure  that  the 
test  tube  or  saucer  is  clean.  Prepare  in  your  note-book  a 
table  like  the  following,  and  fill  in  under  each  head  the  names 
of  the  foods  you  have  proved  to  contain  or  to  be  without 
starch. 


STARCH  PRESENT 

STARCH  ABSENT 

24.  To  test  foods  for  grape  sugar.  Laboratory  Study 
No.  9. 

Materials :  Grape  sugar,  corn  starch,  white  of  egg,  fat  or  oil,  salt, 
water ;  various  food  substances  common  in  home  kitchen ;  Fehling's 
solution  (see  below) ;  test  tubes,  gas  burner  or  alcohol  lamp. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      17 

Preparation  of  Fehling's  Solution:  —  To  make  Fehling's  solution 
dissolve  3  teaspoonfuls  (34.64  grams)  of  pure  pulverized  copper  sul- 
phate (blue  vitriol)  in  a  little  less  than  a  half -pint  of  water  (200  cc.). 
Make  a  second  solution  by  dissolving  in  a  pint  (500  cc.)  of  water 
twelve  heaping  teaspoonfuls  (150  grams)  of  Rochelle  salt  and  3  (5- 
inch)  sticks  of  caustic  soda  (50  grams).  Fehling's  solution  does  not 
keep  for  any  great  length  of  time,  and  hence  must  be  made  up  fresh 
a  short  time  before  it  is  needed.  To  do  this,  thoroughly  mix  two 
volumes  of  the  copper  sulphate  solution  and  five  volumes  of  the 
solution  of  Rochelle  salt  and  caustic  soda,  and  dilute  the  mixture 
with  an  equal  volume  of  water.  It  is  more  convenient  to  prepare 
it  in  small  quantities  from  the  tablets  that  may  be  obtained  of 
druggists.  Before  making  any  tests  boil  a  small  quantity  of  the 
Fehling's  solution  in  a  clean  test  tube.  If  it  retains  its  transparent 
blue  color,  it  is  ready  for  use;  otherwise  a  fresh  supply  must  be 
prepared.1 

1.  Dissolve    a  small  amount    of  grape  sugar    (glucose)  in 

water  in  a  test  tube.  Add  some  Fehling's  solution  and 
boil.  What  change  in  color  do  you  notice? 

2.  Try  the  effect  of  Fehling's  solution  on  each  of  the  other 

food  substances  as  follows :  Put  a  small  amount  of  starch 
into  a  test  tube;  into  a  second  tube  some  white  of  egg; 
into  a  third  tube  some  fat  or  oil;  into  a  fourth  tube  some 
mineral  matter  (salt) ;  and  into  a  fifth  tube  some  water. 
Add  a  little  water  to  each  tube,  then  pour  in  a  small 
amount  of  Fehling's  solution  and  boil  as  in  1  above.  Do 
any  of  the  colors  produced  resemble  at  all  the  color  of 
the  Fehling's  solution  when  it  was  boiled  with  grape  sugar? 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  substance  contains  grape  sugar. 

4.  (Optional.)     Test  as   many   foods    as  you    can    (e.g.  onions, 
grapes,  pears,  granulated  sugar,  honey,  molasses,  parsnip,  raw 
meat,  milk,  egg)  in  the  following  manner :  Put  a  small  amount 
of  a  given  food  into  a  test  tube,  add  a  little  water,  and  a 

1  From  Peabody's  "  Laboratory  Exercises."    Henry  Holt  &  Co., 
New  York, 
c 


18  PLANT  BIOLOGY 

small  spoonful  of  Fehling's  solution,  and  boil.  Before  making 
each  test  make  sure  that  the  test  tube  is  clean.  Prepare  in 
your  note-book  a  table  like  the  following,  and  fill  in  under 
each  head  the  names  of  the  foods  you  have  proved  to  contain 
or  to  be  without  grape  sugar. 


GRAPE  SUGAR  PRESENT 

GRAPE  SUGAR  ABSENT 

. 

25.  To  test  foods  for  proteins  (albuminous  or  nitrogenous 
substances).  —  Laboratory  Study  No.  10. 

Materials :  White  of  egg,  corn  starch,  grape  sugar,  mutton  tallow 
or  other  fat,  salt,  water ;  piece  of  meat,  milk ;  concentrated  nitric 
acid,  ammonia;  test  tubes;  gas  or  alcohol  lamp. 

1.  Pour  a  little  concentrated  nitric  acid  on  a  piece  of  hard 

boiled  egg  in  a  test  tube, 
a.   What  change  in  color  of  the  egg  do  you  observe? 

6.  (Optional.)     Wash  the  egg  with  water,  add  a  little  concen- 
trated ammonia,  and  note  result. 

2.  Try  the  effect  of  nitric  acid  on  each  of  the  other  food  sub- 

stances as  follows:  Put  a  small  amount  of  starch 
into  a  test  tube ;  into  a  second  tube  some  grape 
sugar;  into  a  third  some  mutton  tallow  or  other 
fat ;  into  a  fourth  some  mineral  matter  (salt) ; 
and  into  a  fifth  tube  some  water.  Add  a  little  con- 
centrated nitric  acid  to  each  of  these  foods.  Is 
any  color  produced  like  that  resulting  from  adding 
nitric  acid  to  protein?  (In  case  a  liquid  is  to  be 
tested  with  nitric  acid,  the  mixture  should  be  boiled 
before  deciding  whether  protein  is  present  or  absent.) 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  food  contains  protein. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS      19 

4.  (Optional.)  Prepare  in  your  note-book  a  table  like  the  follow- 
ing, and  place  in  the  proper  columns  the  names  of  the 
foods  tested  in  class. 


PROTEIN  PRESENT 

PROTEIN  ABSENT 

26.  To  test  foods  for  fats.  —  Laboratory  Study  No.  11. 
Suggested  as  home  work. 

Materials :  Butter  or  olive  oil,  corn  starch,  grape  sugar,  piece  of 
boiled  white  of  egg,  salt,  water;  various  foods  in  the  home  kitchen, 
including  nuts. 

1.  Put  on  a  piece  of  paper  a  piece  of  butter  half  the  size  of 

a  pea  (or  a  drop  of  olive  oil).  Put  the  paper  in  a 
warm  place  (e.g.  in  a  hot  oven  or  over  a  heated  radi- 
ator) for  a  few  moments,  then  hold  the  paper  between 
yourself  and  the  light.  How  is  the  paper  affected  by 
the  fat? 

2.  Try  the  effect  of  each  of  the  other  food  substances  (starch, 

grape  sugar,  piece  of  boiled  egg,  i.e.  protein,  salt,  i.e. 
mineral  matter,  water)  on  paper,  by  adding  an  equal 
quantity  (half  the  size  of  a  pea)  of  each  to  separate 
pieces  of  paper.  Put  the  pieces  of  paper  in  a  warm 
place  as  in  1  above.  Hold  each  piece  between  yourself 
and  the  light.  Do  any  of  these  food  substances  affect 
the  paper  as  did  the  fat  ? 

3.  From  the  preceding  experiments  state  how  you  can  de- 

termine whether  or  not  a  food  contains  fat. 

4.  (Optional.)     Prepare  in  your  note-book  a  table  like  the  follow- 

ing, and  place  in  the  proper  columns  the  names  of  the  foods 
tested  at  home  or  in  class. 


20  PLANT  BIOLOGY 


FAT  PRESENT 

FAT  ABSENT 

NOTE.  In  case  a  food  which  is  being  tested  may  possibly  contain 
a  small  amount  of  fat,  the  food  should  be  pulverized,  shaken  in  a 
test  tube  with  ether  or  benzine  (to  dissolve  out  the  fat),  and  allowed 
to  stand  for  24  hours.  The  clear  liquid  should  then  be  poured  upon 
paper,  and  the  ether  or  benzine  allowed  to  evaporate. 

Caution.  Never  handle  ether  or  benzine  near  a  flame  or  hot  stove, 
since  the  vapor  of  these  substances  is  very  inflammable. 

27.  To  test  foods  for  mineral  matter.     Laboratory  Study 
No.  12.     Demonstration. 

Materials:  Salt,  corn  starch,  grape  sugar,  piece  of  boiled  egg, 
butter  or  fat,  water. 

1.  Place  a  piece  of  salt  half  the  size  of  a  pea  on  an  old  cook- 

ing spoon  and  heat  over  as  hot  a  flame  as  possible. 
Does  the  salt  burn  and  disappear? 

2.  In  the  same  manner  try  the  effect  of  heat  on  the  other 

food  substances  (starch,  grape  sugar,  white  of  egg,  fat, 
water) .    Do  any  of  these  substances  burn  or  disappear  ? 

3.  From  the  preceding  experiments  state  how  you  can  deter- 

mine whether  or  not  a  food  contains  mineral  matter. 

4.  (Optional  home  work.)     Test  at  home  in  the  same  manner  as 

described  in  1  above  a  match  stick  and  a  leaf.      Do  these 
plant  materials  contain  mineral  matters  ?     How  do  you  know  ? 

28.  To  test  foods  for  water.  —  Laboratory  Study  No.  13. 
Home  work. 

1.  Warm  a  little  water  on  a  spoon  and  place  over  it  a  dry, 
cool,  tumbler.  What  do  you  see  on  the  inside  of  the 
glass?  How,  then,  can  you  tell  whether  or  not  water 
is  found  in  a  given  food? 


COMPOSITION  OF  LIFELESS  AND  LIVING    THINGS      21 


2.  (Optional.)     Test  as  many  foods  as  you  can  by  warming  in  turn 

a  small  quantity  of  each  in  a  spoon  (without  letting  the  food 
burn),  and  holding  over  the  spoon  a  dry,  cool  tumbler. 
What  do  you  learn  as  to  the  presence  of  water  in  foods  ? 

3.  (Optional  Demonstration.)     To  determine  the  amount  of  water 

in  potatoes: 

a.  Remove  a  thin  layer  of  peel  from  a  potato,  weigh  the  potato, 
and  lay  it  aside  in  a  warm  dry  place  (protected  from  mice). 
Weigh  each  day,  and  fill  out  in  your  note-book  for  each 
day  the  first,  third,  and  fifth  columns  in  a  table  like  the 
following : 


WEIGHT  OF  POTATO 

Loss  OF  ORIGINAL  WT. 

PER  CENT  OF  Loss 

Without 
Peel 

With 
Peel 

Without 
Peel 

With 
Peel 

Without 
Peel 

With 
Peel 

First  day 
Second  day 
Third  day 
Fourth  day 
etc. 



b.  Secure  a  second  potato  about  the  same  size  as  the  first,  weigh 

it  each  day,  and  place  it  beside  the  potato  that  was  peeled. 
Record  results  and  percentages  for  each  day  in  second, 
fourth,  and  sixth  columns  of  preceding  table. 

c.  Which  of  the  two  potatoes  decreases   in   weight   the  more 

rapidly  ?  Almost  all  the  loss  of  weight  is  due  to  the  evapo- 
ration of  water;  what  do  you  infer,  therefore,  as  to  one 
use  of  the  peel  ? 

d.  Continue  to  weigh  the  potato  without  the  peel  at  intervals 

until  there  is  no  further  loss.  What  percentage  of  potato 
is  water?  When  potatoes  are  bought  at  $3  per  barrel, 
how  much  of  this  sum  is  paid  for  water  ? 


22  PLANT  BIOLOGY 


IV.     MANUFACTURE  OF  THE  FOOD  SUBSTANCES  BY  PLANTS 

29.  Is  starch  present  in  the  green  leaves  of  a  plant  that 
has  been  exposed  to  sunlight?  —  Laboratory  Study  No.  14. 

Take  several  leaves  from  a  vigorous  plant  (e.g.  geranium, 
hydrangea)  which  has  been  exposed  to  bright  sunlight  for 
a  number  of  hours.  Boil  them  a  few  moments  in  a  large  test 
tube  or  flask  of  water ;  pour  off  the  water,  add  alcohol,  and 
boil  carefully  over  a  piece  of  wire  gauze  or  asbestos  until  all 
the  green  coloring  matter  has  been  removed.  Rinse  the  leaves 
in  water,  add  iodine  solution,  and  spread  the  leaves  on  saucers, 
or  in  Petri  dishes. 

1.  Describe  in  your  own  words  how  the  experiment  was 

performed. 

2.  Is  starch  present  in  the  leaves  ?     How  do  you  know  ? 

3.  Why  was   it   necessary   to   remove   the   green   coloring 

matter  from  the  leaves  before  testing  for  starch?     (If 
you  are  in  doubt,  add  some  iodine  to  green  leaves.) 

4.  (Optional.)     How  may  grass  stains  be  removed  from  clothing  ? 

30.  Is  starch  present  in  the  green  leaves  of  a  plant  that 
has  been  deprived  of  sunlight?1  —  Laboratory  Study  No.  15. 

Put  a  vigorous  plant  (e.g.  fuchsia,  squash,  sunflower,  or 
bean  seedling)  in  darkness  for  48  hours  or  more.  Remove 
several  leaves,  and  treat  them  as  described  in  29  above. 

1.  State  briefly  how  the  preparation  of  this  experiment  dif- 

fers from  that  in  the  previous  experiment. 

2.  Give  your  observation  and  conclusion. 

3.  State,  therefore,  whether  sunlight  is  or  is  not  necessary 

for  the  manufacture  of  starch  in  green  leaves. 

31.  Is  starch  present  in  colorless  portions  of  green  leaves? 
—  Laboratory  Study  No.  16. 

1  A  most  suggestive  series  of  experiments  on  the  formation  of 
starch  in  green  leaves  is  found  in  the  Botanical  Gazette  for  September, 
1909,  pp.  224-228,  by  Sophia  Eckerson,  of  Smith  College. 


COMPOSITION  OF  LIFELESS  AND  LIVING   THINGS     23 


Secure  a  plant  having  some  portions  that  are  colorless  (e.g. 
striped  grass).  Expose  the  plant  to  sunlight  for  two  or  three 
hours,  then  remove  several  leaves  and  test  them  in  the  same 
manner  as  described  in  29  above. 

1.  State  briefly  how  the  preparation  of  this  experiment 

differs  from  that  of  the  two  preceding  experiments. 

2.  What  is  your  observation  and  conclusion  as  to  the  pres- 

ence of  the  starch  in  the  green  and  colorless  portions? 

3.  State,  therefore,  whether  green  material  is  or  is  not  neces- 

sary for  the  manufacture  of  starch. 

This  green  material  in  leaves  is  called  chlorophyll  (from 
Greek  chloros  =  green  +  phidlon  =  leaf). 

32.  Is  carbon  dioxid  necessary  for  starch  manufacture  in 
leaves?  —  Laboratory  Study  No.  17. 

Secure  two  vigorous  potted  plants,  two  bell-jars  large 
enough  to  go  over  the  plant  and  pot,  and  two  trays  or  other 
receptacles  having  a  greater  di- 
ameter than  that  of  the  bell-jar. 
Place  the  plants  in  darkness  for  24 
hours  at  least,  so  that  the  leaves 
may  be  free  from  starch  (see  30 
above).  Now  test  the  leaves  of 
both  plants  to  make  sure  they 
are  free  from  starch.  Into  one 
tray  pour  a  quantity  of  lime  water 
and  into  the  other  tap  water. 
Put  the  plants  on  supports  of 
some  kind  so  that  the  pots  will 
not  touch  the  liquid,  and  cover 

With  the  bell-jars.  (See  Fig.  3.)  FIG.  3.  — Apparatus  for  demon- 
Be  sure  that  the  edges  of  the  bell- 
jars  are  covered  with  the  liquid, 
so  that  no  air  can  enter  the  jars.  Place  both  preparations 
where  the  plants  can  get  no  sunlight  for  24  hours  in  order 
to  give  time  for  the  absorption  of  carbon  dioxid  in  the  jar 
with  the  lime  water.  Place  both  preparations  in  strong 
sunlight  for  several  hours. 


strating  the  relation  of  carbon 
dioxid  to  starch  manufacture. 


24  PLANT  BIOLOGY 

1.  Describe  the  preparation  of  the  experiment. 

2.  Examine  the  lime  water  inside  the  bell-jar.     What  proof 

have  you  that  carbon  dioxid  has  been  absorbed  ? 

3.  Remove  a  leaf  from  each  of  the  plants  and  test  for  starch. 

Tell   what   was   done    and    state   your   observations. 
Which  leaf,  therefore,  contains  starch? 

4.  What  is  your  conclusion  as  to  the  necessity  of  carbon 

dioxid  for  starch  manufacture? 

5.  What  chemical  elements  that  are  present  in  starch  might 

be  furnished  by  the  carbon  dioxid  (CO2)  ? 

6.  The  other  raw  material  needed  by  plants  for  the  manu- 

facture of  starch  is  water  (H20) .     What  third  chemical 
element  found  in  starch  must  be  furnished  by  water? 

7.  Now  name  the  two  raw  materials  used  by  plants  in  the 

manufacture  of  starch  and  state  the  chemical  elements 
which  each  can  furnish. 

33.  Manufacture  of  carbohydrates.  —  The  substance  first 
made  by  the  combination  of  carbon,  hydrogen,  and  oxygen 
in  the  leaves  is  not  starch,  but  a  simple  carbohydrate  which 
is  then  made  into  grape  sugar.     When  the  plant  manufactures 
more  sugar  than  it  needs  for  immediate  use,  the  surplus  is 
changed  to  starch,  and  this  is  what  we  have  found  stored  in 
the  leaves. 

34.  Manufacture  of  proteins.  —  We  have  already  learned 
that  proteins  contain  carbon,  hydrogen,  oxygen,  nitrogen, 
and  usually  sulphur  and  phosphorus  (see  21).     The  plant, 
therefore,  must  somehow  obtain  these  elements  in  order  to 
manufacture    proteins.     It    has    been    proved    that    plants 
manufacture  sugar,  and  this  probably  supplies  the  necessary 
carbon,  hydrogen,  and  oxygen.     The  nitrogen  that  is  needed 
is  furnished  by  compounds  containing  nitrogen  such  as  salt- 
peter (potassium  nitrate,  KNOs),  and  the  sulphur  and  phos- 
phorus are  secured  from  mineral  compounds  known  as  sul- 
phates and  phosphates.     These  compounds  are  derived  from 
soil  water.     From  these  compounds,  namely,  sugar  and  the 


COMPOSITION   OF  LIFELESS  AND  LIVING   THINGS      25 

mineral  matters  containing  nitrogen,  sulphur,  and  phos- 
phorus obtained  from  the  soil,  the  living  plant  manufactures 
protein. 

35.  Do  green  plants  give  off  a  gas  in  sunlight?  —  Labora- 
tory Study  No.  18. 

Into  a  glass  cylinder  containing  water  fresh  from  the  faucet 
put  a  small  amount  of  water  plant  (Elodea,  Spirogyra,  or 
Milfoil),  holding  it  to  the  bottom  of  the  tall  jar  by  means  of 
a  weight  if  necessary.  Stand  the  cylinder  in  direct  sunlight. 

1.  Describe  the  preparation  of  the  experiment. 

2.  What  do  you  observe  coming  off  from  the  plant  ?     (These 

bubbles  of  gas  have  been  proved  to  be  composed  of 
oxygen.) 

36.  Do  green  plants  give  off  a  gas  when  deprived  of  sun- 
light? —  Laboratory  Study  No.  19. 

Place  the  glass  cylinder  prepared  as  directed  t above  in 
darkness  for  several  hours  (or,  still  better,  a  second  cylinder 
should  be  used  for  comparison). 

1.  In  what  respects  do  Experiments  18  and  19  differ? 

2.  Do  you  see  any  bubbles  as  long  as  the  cylinder  is  kept 

in  the  dark? 

3.  Under  what  condition,  therefore,  does  a  green  plant  give 

off  oxygen? 

37.  The  oxygen  supply  for  animals.  —  We  have  seen  that 
starch  is  made  of  carbon  dioxid  (CO2)  and  water  (H2O).     By 
repeated  experiments  biologists  have  proved  that  in  the  pro- 
cess of  manufacturing  carbohydrates  more  oxygen  is  present 
in  the  CO2  and  H20  than  is  needed.     This  is  the  oxygen  we 
have  seen  given  off  by  the  green  water  plant  in  sunlight. 
Every  green  plant  gives  off  oxygen  into  the  air  when  manu- 
facturing carbohydrates.     Hence,  in  this  process  the  carbon 
dioxid  is  constantly  being  taken  from  the  air  and  a  fresh 
supply  of  oxygen  set  free. 


CHAPTER  III 


THE   STRUCTURE  OF   PLANTS 


38.    The  parts  of  a  plant.  —  Laboratory  Study  No.  20. 

Materials:  A  well-developed  bean  plant  or  other  seedling  or  a 
weed,  for  each  two  pupils ;  one  or  more  plants  with  flowers  and  if 
possible  with  fruits  for  demonstration. 

Nearly  all  the  plants  with  which  we  are  most  familiar 
consist  of  at  least  three  'kinds  of 
parts,  namely,  roots,  stems,  and  leaves 
(Fig.  4). 

1.  Name  and  describe  as  to  color  and 

form  the  parts  of  the  plant  that 
grew  beneath  the  ground. 

2.  How  does  the  stem  differ  from  the 

root  as  to  color  and  direction  of 
growth?  What  parts  of  the 
plant  above  ground  are  attached 
to  the  stem? 

3.  How  does  the  main  part  of  the  leaf 

differ  in  form  from  the  root  or 
the  stem? 

4.  Make  a  drawing,  natural  size,  of  the 

plant  you  are  studying,  labeling 
ground  level,  roots,  stem,  leaf. 

5.  On  the  plants  used  for  demonstra- 

tion, what  parts  besides  those 
named  above  do  you  find  ?  How 
do  the  colors  of  these  parts  differ 
from  the  color  of  the  rest  of  the 
plant? 
26 


FIG.  4.  —  Roots,  stems, 
leaves,  flowers,  and  fruits 
of  a  buttercup  plant. 


THE  STRUCTURE  OF  PLANTS  27 

39.  Organs  and  functions.  —  From  our  laboratory  study 
we  have  learned  that  a  common  plant  consists  of  roots,  stems, 
and  leaves,  and  that  at  certain  seasons  of  the  year  flowers 
and  fruits  are  present.     To  each  of  these  various  parts  is 
given  the  name  organ.     Roots  are  useful  to  a  plant,  for  one 
thing,  because  they  hold  it  in  the  ground,  while  stems  support 
the  leaves,  flowers,  and  fruits.     In  fact  every  organ  of  a 
plant  has  some  work  to  do,  and  this  work  is  called  its  func- 
tion.    Hence,  we  may  define  an  organ  as  a  part  of  a  plant  that 
has  a  certain  function  or  functions  to  perform. 

40.  Microscopic  structure  of  plants.  —  When  one  exam- 
ines by  the  aid  of  a  compound  microscope  a  small  portion 
of  any  of  the  organs  of  common  plants,  one  finds  that  each 
organ  is  composed  of  many  smaller  portions  too  minute  to  be 
seen  with  the  unaided  eye.     These  tiny  divisions  are  called 
cells.     We  shall  now  attempt  to  become  familiar  by  the  use 
of  the  compound  microscope  with  the  appearance  of  several 
kinds  of  plant  cells. 

41.  Study  of  plant  cells.  —  Laboratory  Study  No.  21. 

Materials:  (1)  Slides  prepared  as  follows :  Cut  a  layer  of  an  onion 
bulb  into  small  squares,  and  strip  off  from  the  inner  surface  of  each 
square  a  very  thin  layer.  Place  it  on  a  glass  slide  and  add  a  drop 
of  water.  (If  it  is  desirable  to  keep  the  slides  for  several  hours, 
put  glycerin  diluted  with  water  over  the  onion  cells.)  Cover  each 
thin  membrane  with  a  cover  glass.1  (2)  Prepared  or  freshly  cut 
thin  sections  of  roots,  stems,  and  leaves. 

1.  By  the  aid  of  the  low  power  of  the  compound  microscope, 
examine  the  slide  prepared  as  directed  in  (1)  under 
materials.  Note  that  the  thin  membrane  is  com- 
posed of  a  large  number  of  tiny  spaces  each  in- 

1  The  authors  are  indebted  to  Miss  Elsie  M.  Kupfer,  Head  of 
Department  of  Biology  of  Wadleigh  High  School,  New  York  City, 
for  suggesting  this  admirable  material  for  cell  study. 


28  PLANT  BIOLOGY 

closed  by  lines  more  or  less  dark  in  color  called 
cell-walls.  (These  parts  are  usually  seen  more  clearly 
if  the  light  is  largely  excluded  by  closing  the  dia- 
phragm in  the  stage.) 

a.  Describe  the  general  appearance  of  the  membrane, 

stating  of  what  it  is  composed. 

b.  State  whether  or  not  the  cells  in  the  various  parts  of 

the  membrane  differ  in  size  and  shape. 

2.  The  cell-wall  incloses  a  semifluid  substance  which  makes 

up  the  cell-body.  Describe  the  appearance  of  the 
cell-body. 

3.  Within  the  cell-body,  often  near  the  center  of  the  cell, 

is  usually  a  tiny  object  called  the  nucleus.  Describe 
the  location,  shape,  and  color  of  the  nucleus. 

4.  Make  a  drawing  of  three  or  four  adjacent  cells,  several 

times  as  large  as  they  appear  under  the  microscope. 
Label  cell-wall,  cell-body,  cell-nucleus. 

5.  (Demonstration.)     Secure  some  growing  sprays  of  Elodea 

(a  common  water  plant) .  Pull  off  one  of  the  youngest 
leaves  near  the  tip  end,  put  it  on  a 
slide  with  a  drop  of  water,  and  cover 
with  a  cover  glass.  Let  the  prepara- 
tion stand  in  a  warm  place  for  a  time. 

Examine  with  the  high  power  the  cells  of 
which  this  leaf  is  composed. 

Within  each  cell  note  some  green  bodies 
called  chlorophyll  bodies  (from  Greek, 
meaning  leaf  green).  These  are  the 
bodies  which  aid  in  starch  manufac- 
ture in  green  leaves.  (See  31.) 

a'  Describe  tne  form>  color>  and  use  of 
chlorophyll  bodies. 

b.  Carefully   watch   the   chlorophyll   bodies   in    several 

cells  and  describe  any  movements  you  see.  These 
movements  show  that  the  substance  of  the  cell  is 
in  motion,  and  is  carrying  the  chlorophyll  bodies 
along  with  it. 

c.  Make  a  drawing  at  least  2  inches  long  of  one  of  the 

cells  with  its  chlorophyll  bodies.     Label  cell-wall, 


THE  STRUCTURE  OF  PLANTS 


29 


cell- 
wall 


chlorophyll  bodies,  and  show  by  arrows  the  direction 
of  their  movements. 

6.  (Demonstration.)  Examine  with  the  low  power  of  the 
microscope  the  sections  of  root,  stem,  and  leaf,  or 
study  Figures  11, 12, 15, 22.  Write  a  paragraph  on 
the  microscopic  structure  of  root,  stem,  and  leaf. 

(Optional.)     Make  a  drawing  of  four  or  five  cells  from 
each  of  the  organs  studied. 

42.  Cells  and  protoplasm.  —  Under  the  microscope  cells 
at  first  appear  to  be  only  plane  surfaces  surrounded  by  lines. 
In  reality,  however,  each  cell  has 
not  only  length  and  breadth,  but 
also  thickness,  and  each  cell  is 
covered  on  all  sides  by  a  cell-wall 
which  is  composed  of  a  lifeless 
substance  known  as  cellulose. 
This  wall  is  often  so  transparent 
that  we  can  look  through  it  and 
see  the  cell-body  and  nucleus 
within  (Fig.  6). 

The  discovery  of  these  minute 
bodies  of  which  organs  are  com-  ceii-nucieus.... 
posed  was  not  made  until  about 
the  middle  of  the  last  century 
(1848).  With  the  rather  imper- 
fect microscopes  then  in  use  the 
two  discoverers,  Schleiden  and 
Schwann,  could  see  the  cell-walls 
only,  and  they  did  not  know,  as 
we  now  know,  that  the  most  im- 
portant part  of  the  cell  is  not  the  lifeless  wall  of  cellulose, 
but  the  living  substance  which  is  found  inside  the  cell -wall, 
making  up  a  large  part  of  the  cell-body  and  cell-nucleus. 


protoplasm 
of  cell-body 


FIG.  6.  —  Plant  .cell.  The  spaces 
in  the  cell-body  are  filled  with 
cell-sap. 


30  PLANT  BIOLOGY 

To  this  substance  is  given  the  name  protoplasm.  We  know 
now  that  the  living  substance  or  protoplasm  is  the  essential 
part,  while  the  wall  may  be  missing,  so  that  in  such  a 
case  there  is  no  resemblance  to  a  cell  or  box.  Biologists 
now  understand  a  cell  to  be  a  bit  of  protoplasm  (cell-body)  con- 
taining a  nucleus  (which  is  a  denser  portion  of  the  protoplasm) . 

Protoplasm,  when  examined  with  the  highest  powers  of  the 
microscope,  appears  as  a  colorless,  semifluid  substance,  in 
which  are  often  seen  solid  particles  or  granules,  which  are 
probably  little  masses  of  food.  The  nucleus,  as  already 
stated,  is  commonly  found  near  the  center  of  the  cell,  and  is 
composed  of  protoplasm  denser  than  the  protoplasm  of  the 
body  of  the  cell.  The  appearance  and  composition  of  the 
protoplasm  may  be  well  represented  by  raw  white  of  egg ;  but 
in  making  this  comparison  one  should  bear  in  mind  that  the 
white  of  an  egg  is  not  living  substance. 

Within  the  cell,  too,  and  occupying  some  of  the  space  out- 
side the  nucleus,  especially  in  plant  cells,  is  cell-sap,  which  is  a 
lifeless  fluid  composed  of  water  in  which  are  dissolved  the  food 
substances  (such  as  sugar  and  mineral  matters)  used  by  cells 
in  their  growth  and  repair,  and  in  the  various  kinds  of  work 
which  they  carry  on  (Fig.  6). 

43.  Assimilation,  growth,  and  cell  division.  —  To  make 
protoplasm  the  plant  must  have  proteins,  water,  and  addi- 
tional compounds  containing  iron,  calcium,  and  several  other 
chemical  elements.  But  only  protoplasm  has  the  power  to 
combine  these  compounds  in  such  a  way  as  to  form  living 
matter.  Bearing  in  mind  the  facts  we  learned  in  studying 
food  manufacture  (33  and  34),  we  see  that  the  plant  begins 
with  simple  substances,  water  and  carbon  dioxid,  and  manu- 
factures a  more  complex  substance,  sugar.  It  uses  this  and 
other  substances  to  make  a  still  more  complex  substance, 


THE  STRUCTURE  OF  PLANTS 


31 


protein,  and  finally  ends  by  making  the  most  complex  of  all, 
protoplasm.  But,  except  in  rare  cases,  all  plants  must  have 
compounds  to  start  with ;  they  cannot  make  any  of  these 
nutrients  or  protoplasm  from  chemical  elements. 

And  thus  we  learn  that  food  materials  are  gradually 
changed  by  protoplasm  into  living  substance  like  itself.  To 
this  process  is 
given  the  name 
assimilation 
(Latin,  ad  =  to 
= similis  =like) . 
As  a  result 
of  the  process 
of  assimilation 
the  amount  of 
protoplasm  of 
course  increases 


B  C 

FIG.  7.  —  Cell  division. 

A,  cell  before  division ;   B,  cell  with  divided  nucleus ;   C,  single 
cell  that  has  divided  into  two  cells. 

grows.     Were 

this  process  to  continue  indefinitely,  cells  would  become 
large  in  size.  This,  however,  does  not  occur;  for  when 
a  cell  reaches  its  normal  size,  the  nucleus  divides,  and  the 
halves  separate  from  each  other  to  form  two  nuclei.  The 
cell-body  now  divides  into  two  parts,  and  cell-walls  are 
formed  between  the  two  cells  (Fig.  7).  Thus  are  produced 
two  cells,  each  having  its  own  nucleus,  and  these  in  turn  as- 
similate, grow,  and  divide.  In  this  way  the  number  of  cells 
increases  with  the  growth  of  the  plant. 


CHAPTER  IV 


OSMOSIS   AND   DIGESTION 


Materials :  Four  thistle  tubes,  four  wide-mouthed  bottles ;  honey, 
molasses,  or  a  thick  solution  of  grape  sugar ;  starch  (arrowroot  if 
possible),  diastase ;  white  of  egg,  peptone ;  iodine,  Fehling's  solution, 
nitric  acid.  Procure  the  intestines  of  calf  or  beef,  wash  them  thor- 
oughly inside  and  out,  and  inflate  them  by  the  aid  of  a  glass  tube. 
Tie  at  intervals  of  two  or  three  feet,  and  allow  this  animal  mem- 
brane to  dry.  Cut  off  pieces  about  two  inches  long,  and  slit  open 
each  of  the  pieces  thus  obtained.  Membrane 
prepared  in  this  way  may  be  kept  in  closed 
bottles  for  years.  If  desired,  the  pieces  of 
membrane  may  be  used  at  once  without  dry- 
ing. Sausage  coverings  that  have  been  pre- 
served in  salt  may  be  thoroughly  washed, 
dried,  and  used. 

Thistle  tube  No.  L—  Hold  one  of  the  thistle 
tubes  upright,  closing  the  smaller  end  by  press- 
ing on  it  with  the  thumb.  Into  the  larger 
end  pour  the  honey,  molasses,  or  grape  sugar 
solution,  which  has  been  sufficiently  warmed  to 
pour  easily.  Half  fill  the  tube  and  nearly  fill 
the  bulb.  Moisten  one  of  the  pieces  of  intestine 
and  tie  it  tightly  over  the  bulb  of  the  thistle 
tube  so  that  none  of  the  liquid  can  escape. 
Wash  off  any  of  the  liquid  from  the  outside  of 
the  membrane,  then  dry  it  with  a  blotter,  and 
hold  the  thistle  tube  bulb  down  for  several  minutes  to  make  sure 
that  the  grape  sugar  solution  does  not  leak  out.  Now  stand  the 

32 


FIG.  8.  —  Apparatus 
for  thistle  tube 
No.  1  in  osmosis 
experiment. 


OSMOSIS  AND  DIGESTION  33 

tube,  membrane  down,  in  one  of  the  wide-mouthed  bottles  'and  fill 
it  with  water  up  to  the  neck.  Add  grape  sugar  solution  to  the  thistle 
tube  until  the  level  of  the  water  in  the  bottle  and  that  of  the 
liquid  in  the  thistle  tube  is  the  same.  Connect  a  long  piece  of 
glass  tubing  to  the  upper  end  of  the  inverted  thistle  tube,  and 
support  this  tube  in  a  vertical  position,  so  that  the  membrane  does 
not  touch  the  bottom  of  the  bottle  (Fig.  8) . 

Thistle  tube  No.  2.  —  Set  up  a  control  experiment  exactly  like 
No.  1,  except  that  water  should  be  put  into  the  thistle  tube  as  well 
as  in  the  bottle. 

44.  Will  water  pass  through  a  membrane  ?  —  Laboratory 

Study  No.  22. 

1.  Give  in  your  own  words  a  description  of  the  way  thistle 

tube  No.  1  was  prepared,  making  a  diagram  of  the 
apparatus,  and  labeling  level  of  water  in  bottle 
and  of  grape  sugar  solution  in  thistle  tube  at  the 
beginning  of  the  experiment. 

2.  At  the  end  of  a  few  hours  compare  the  level  of  the  liquid 

in  thistle  tube  No.  1  with  the  level  in  thistle  tube 

No.  2. 

a.   How  many  inches  has  the  grape  sugar  risen  in  No.  1? 
6.    Is  there  a  similar  rise  in  the  water  in  thistle  tube 

No.  2? 

c.  What  must  have  passed  into  thistle  tube  No.  1  to 

cause  the  liquid  to  rise? 

d.  Through  what  must  this  liquid  have  passed  to  get 

into  the  thistle  tube? 

3.  Do  you  conclude,  therefore,  that  water  will  or  will  not 

pass  through  a  membrane  ? 

45.  Will  grape  sugar  pass  through  a  membrane?  —  Labor- 
atory Study  No.  23. 

1.  At  the  end  of  a  few  hours  test  the  liquid  in  bottle  No.  1 
by  putting  a  glass  tube  to  the  bottom  of  the  bottle, 
pressing  the  thumb  over  the  top  of  the  tube,  and 
removing  the  sample  of  liquid  thus  obtained  to  a 
clean  test  tube;  add  Fehling's  solution  and  boil. 


34  PLANT  BIOLOGY 

a.   Describe  what  was  done. 

6.   Is  grape  sugar  present  now?     How  do  you  know? 

c.    What  must  have  happened  to  produce  this  result? 

2.  We  have  now  proved  that  two  different  liquids  have 

passed  through  the  membrane. 

a.  Name  these  two  liquids. 

b.  Which  of  these  two  liquids  has  passed  through  the  mem- 

brane in  the  greater  quantity  ?     How  do  you  know  ? 

c.  Which  of  these  two  liquids  is  the  thicker  or  denser  ? 

d.  By  a  great  many  experiments  it  has  been  proved  that, 

when  any  two  liquids  of  different  density  are  sep- 
arated by  a  plant  or  animal  membrane,  results  sim- 
ilar to  those  noted  above  follow.  To  this  inter- 
change of  liquids  is  given  the  name  osmosis.  In  this 
process  of  osmosis,  is  the  greater  flow  of  liquid  from 
the  less  dense  to  the  more  dense,  or  from  the  more 
dense  to  the  less  dense? 

e.  Why  did  not  the  water  rise  in  thistle  tube  No.  2  ? 

3.  Do  you  conclude,  therefore,  that  grape  sugar  will  or  will 

not  pass  through  a  membrane? 

46.    Osmosis  in  living  cells.  —  Laboratory  Study  No.  24. 

Peel  a  potato  and  then  cut  several  cross  sections  about 
inch  in  thickness.  Allow  these  sections  to  stand  in  the 
air  until  they  bend  readily.  Half  fill 
one  tumbler  with  water  and  a  second 
tumbler  with  a  strong  solution  of 
sugar  or  salt.  Place  some  of  the 
sections  in  each  of  the  two  tumblers 
and  leave  them  for  several  hours. 

1.  Describe  the  preparation  of  this 

experiment. 

2.  Remove  a  section  of  potato  from 

FIG.    S        -  Cells    from    a  each       f    th      R      idg          d    fe      d 

potato,    showing    cell-  ^  *,,         , 

walls,     cell-sap,     and  them-    Compare  the  change  that 

starch  grains  of  differ-  has  taken  place  in  the  rigidity  or 

ent  sizes.  stiffness  of  the  sections  placed 

in  the  strong  solution  and  those  in  the  tap  water. 


OSMOSIS  AND  DIGESTION  35 

3.  Potato  sections,  like  those  of  all  parts  of  living  plants, 
are  composed  of  a  large  number  of  living  cells,  each  one 
inclosed  by  a  cell  membrane  (Fig.  9). 
Call  to  mind  what  you  learned  in  45,  and  state  why  the 
cells  become  even  more  flabby  in  one  solution  and  more 
rigid  in  the  other. 

47.  Will  starch  pass  through  a  membrane  ?  —  Laboratory 
Study  No.  25. 

Thistle  tube  No.  3.  —  Put  into  a  third  thistle  tube  a  mixture  of 
starch  and  water,  cover  the  bulb  with  a  membrane,  and  invert  in  a 
bottle  of  water,  as  already  directed  for  the  first  thistle  tube.  See 
that  the  level  of  the  liquid  is  the  same  in  all  of  the  experiments. 

1.  In  what  respects  does  the  preparation  of  thistle  tube 

No  3  resemble  that  of  No.  1?     How  do  the  two 
experiments  differ? 

2.  At  the  end  of  a  few  hours  test  the  liquid  in  bottle  No.  3 

by  removing  a  sample  to  a  test  tube  (as  already 
directed  in  45),  and  adding  iodine  solution. 

a.  Is  starch  present?     How  do  you  know? 

b.  What  is  your  conclusion  as  to  the  possibility  of  starch 

passing  through  a  membrane? 

3.  What  have  these  experiments  in  osmosis  taught  you  as 

to  one  difference  between  starch  and  grape  sugar? 

48.  Definitions  and  applications.  —  The  experiments  we 
have  been  performing  have  most  important  relations  to  the 
study  of  all  living  plants  and  animals.     We  may  give  the 
following  as  a  definition  of  the  process  we  are  considering: 
Osmosis  is  the  interchange  of  liquids  of  different  density  that  are 
separated  by  a  plant  or  an  animal  membrane,  and  in  this  pro- 
cess the  greater  flow  is  always  from  the  less  dense  to  the  more 
dense. 

We  shall  constantly  refer  to  this  principle  of  osmosis,  and 
we  shall  find  that  it  explains  in  large  measure  the  absorption 
of  soil  water  by  roots,  the  transfer  of  sap  from  one  part  of  a 


36  PLANT  BIOLOGY 

plant  to  another,  as  well  as  the  processes  by  which  the  blood 
of  animals  obtains  and  gives  off  food  to  various  cells  of  the 
body. 

By  the  preceding  experiments  we  have  proved  that  there  are 
two  classes  of  food  substances.  One  kind  (including  water  and 
grape  sugar)  will  readily  pass  through  a  membrane  by  osmosis ; 
the  other  kind  (represented  by  starch)  will  not.  In  our  study 
of  cells  we  learned  that  the  protoplasm  or  living  substance  is 
inclosed  by  a  cell-wall  which  separates  one  cell  from  another. 
Now  if  cells  are  to  make  use  of  the  food  materials  manufac- 
tured in  other  parts  of  the  plant,  each  food  substance  must  be 
in  such  a  form  that  it  can  pass  through  these  cell-membranes. 
It  is  evident  that  water  and  grape  sugar  can  do  this.  We 
find,  however,  large  quantities  of  starch  stored  in  cells 
(Fig.  9).  Hence,  to  be  available  for  use  in  other  cells,  some 
change  must  be  made  in  this  food  substance  before  it 
can  be  transferred  from  cell  to  cell.  We  shall  now  show  by 
experiment  what  this  change  is. 

49.    How  starch  is  made  ready  to  pass  through  a  membrane. 

—  Laboratory  Study  No.  26. 

Into  each  of  two  test  tubes  put  a  small  amount  of  starch 
(arrowroot  starch  if  it  can  be  obtained),  add  some  water, 
shake,  and  boil.  To  the  starch  mixture  in  one  test  tube  add 
some  diastase,  equal  in  amount  to  one-half  the  size  of  a  pea. 
(Diastase  is  a  chemical  substance  produced  or  secreted  by 
the  protoplasm  of  plant  cells.)  Put  the  two  test  tubes  side 
by  side  in  a  warm  place  for  5  minutes  if  arrowroot  starch, 
24  hours  if  corn  starch  is  used,  then  test  a  small  amount  of 
the  mixture  in  each  test  tube  by  adding  a  few  drops  of  iodine. 

1.  Describe  in  your  own  words  what  has  been  done. 

2.  In  which  test  tube  do  you  find  starch  present  ? 

3.  Now  test  with  Fehling's  solution  a  small  quantity  of 

each  mixture.     In  which  tube  do  you  find  grape  sugar  ? 


OSMOSIS  AND  DIGESTION  37 

4.  What  do  you  conclude,  therefore,  as  to  the  effect  of  dias- 

tase on  starch? 

5.  Why  is  this  change  necessary  if  starch  is  to  be  used  by 

plants? 

50.  To  prove  that  starch  is  made  soluble  in  growing  plants. 
—  Laboratory  Study  No.  27. 

1.  Pound  two  or  three  corn  grains  into  a  powder  and  put 

some  of  this  corn  meal  into  a  test  tube,  add  water,  and 
boil.  To  one-half  of  the  mixture  add  iodine,  and  to  the 
other  half,  Fehling's  solution,  and  boil.  Give  a  careful 
description  of  the  experiment  and  state  your  observa- 
tions and  conclusions. 

2.  Secure  some  germinating  corn  grains,  cut  them  into  small 

pieces,  and  test  some  of  them  with  Fehling's  solution  as 
in  1  above.  Describe  the  experiment,  stating  your  ob- 
servations and  conclusions. 

3.  The  change  in  starch  that  you  have  described  is  known 

as  digestion.  What  reason  have  you  for  believing  that 
digestion  of  starch  takes  place  when  corn  grains  ger- 
minate ? 

51.  Definition  of  digestion.  —  We  may  define  digestion  as 
the  chemical  change  whereby  insoluble  food  substances  are  made 
ready  to  pass  through  membranes  and  become  ready  for  the  use 
of  protoplasm.     Let  us  now  by  experiment  determine  whether 
or  not  protein  needs  digestion. 

52.  Will  protein  pass  through  a  membrane?  —  Laboratory 

Study  No.  28. 

Thistle  tube  No.  4-  —  Secure  some  white  of  egg,  cut  it  with  scis- 
sors and  mix  it  with  water.  (White  of  egg,  we  found,  contains  a 
large  amount  of  protein.)  Prepare  the  fourth  thistle  tube  in  the 
same  way  as  directed  for  thistle  tube  No.  1 ,  only  using  white  of  egg 
and  water  instead  of  grape  sugar.  See  that  the  level  of  the  liquid 
is  the  same  as  in  thistle  tube  No.  2. 


38  PLANT  BIOLOGY 

1.  In  what  respects  does  the  preparation  of  thistle  tube 

No.  4  resemble  that  of  thistle  tube  No.  1  ?  How  do  the 
two  experiments  differ? 

2.  Allow  the  experiment  to  stand  for  several  hours,  and  then 

remove  with  a  glass  tube  a  sample  of  the  liquid  in 
bottle  No.  4,  and  test  it  by  adding  nitric  acid  and  boil- 
ing. Is  protein  present  ?  How  do  you  know  ? 

3.  Do  you  conclude,  therefore,  that  protein  will  or  will  not 

pass  through  a  membrane  ? 

53.  Digestive  ferments.  —  We  have  stated  that  proto- 
plasm secretes  a  substance  called  diastase,  and  have  shown 
that  this  diastase  will  change  insoluble  starch  to  soluble  grape 
sugar,  which  will  pass  from  one  cell  to  another  by  the  process 
of  osmosis.  Diastase  is  a  substance  known  as  a  digestive 
ferment.  Now  protoplasm  produces  other  digestive  ferments, 
some  of  which  will  change  insoluble  protein  to  a  soluble  sub- 
stance known  as  peptone.  The  latter  will  readily  pass  by  the 
process  of  osmosis  through  a  membrane. 

Fats,  also,  like  starch  and  protein,  are  insoluble  and  can- 
not, therefore,  pass  by  osmosis  through  cell  walls.  To  make 
these  food  substances  available  for  use  they  must  also  be 
changed  by  the  plant  cells  into  such  forms  that  they  may  be 
readily  transferred  from  one  part  of  the  plant  to  another. 
These  changes  are  caused  by  other  chemical  ferments 
duced  by  protoplasm. 


CHAPTER  V 
ADAPTATIONS  OF  THE  NUTRITIVE  ORGANS  OF  PLANTS 

54.  The  nutritive  organs  of  plants.  —  From  our  study  of 
food  manufacture  (29-34)  we  learned  that  the  plant  foods  are 
produced  in  green  leaves.     Before  this  process  of  food  manu- 
facture can  go  on,  however,  the  cells  in  the  leaf  must  be  sup- 
plied with  raw   materials  from  the  air   and  from  the  soil. 
Since  the  roots,  stems,  and  leaves  are  all  concerned  in  food 
making,  these  organs  are  known  as  the  nutritive  organs  of 
plants.     Each  of  these  organs  has  several  functions ;  we  shall 
now  learn  what  some  of  these  functions  are,  and  how  the 
nutritive  organs  are  adapted  for  the  work  they  do. 

I.     THE  STRUCTURE  AND  ADAPTATIONS  OF  ROOTS 

55.  The  structure  of  roots.  —  Laboratory  Study  No.  29. 
A.   Gross  structure  of  roots. 

Select  the  largest  roots  of  a  well-developed  seedling  or  the 
roots  of  common  weeds.  By  means  of  your  thumb  and  finger 
nail  gently  scrape  off  the  outer  layers  from  a  piece  of  one  of 
these  roots.  When  no  more  of  the  material  can  be  easily 
removed  by  this  method,  pick  to  pieces  the  central  part  of 
the  root  which  is  left.  The  outer  layer  you  have  removed  is 
largely  composed  of  the  cells  of  the  cortex,  and  the  central 
part  that  has  been  exposed  is  called  the  central  cylinder. 

1.  Tell  what  you  have  done. 

2.  Which  is  composed  of  the  tougher  and  harder  material, 

the  cortex  or  the  central  cylinder  ? 
39 


40  PLANT  BIOLOGY 

3.  Make  a  diagram  greatly  enlarged  of  a  piece  of  root 
prepared  as  directed  above.  Label  cortex,  central 
cylinder,  fibers  of  central  cylinder. 

B.  Root-hairs. 

Note  to  the  Teacher.  —  Root-hairs  may  be  grown  for  study  as 
follows :  Cover  the  bottom  of  as  many  Petri  dishes  as  are  needed 
with  a  layer  of  blue  blotting  paper.  Soak  the  paper  with  water  and 
lay  several  grains  of  soaked  barley,  oats,  or  corn  upon  the  bottom 
of  each  dish.  Put  the  covered  dishes  in  a  warm  place  for  several 
days.  When  the  root- hairs  have  developed,  wipe  the  moisture  from 
the  inside  of  the  covers,  quickly  replacing  the  latter.  If  Petri  dishes 
are  not  available,  two  clean  glasses  of  any  convenient  size  may  be 
used  instead.  Cover  one  of  the  plates  with  layers  of  wet  blotting 
paper,  put  the  soaked  grains  in  position,  and  cover  with  the  second 
glass,  fastening  the  two  together  with  threads  or  strings.  Stand 
one  end  of  the  preparation  thus  made  in  a  jar  with  enough  water  to 
reach  the  lower  edge  of  the  blotting  paper. 

Examine  first  with  the  naked  eye  and  then  with  a  hand 
magnifier  the  roots  of  sprouted  grains,  developed  as  described 
above.  Notice  tiny  outgrowths  from  the  sides  of  the  roots; 
these  outgrowths  are  called  root-hairs. 

1.  Look  at  the  very  tip  of  the  root  and  state  whether 

root  hairs  are  there  present  or  absent. 

2.  State  whether  the  root-hairs  are  longest  near  the  tip 

or  in  the  direction  of  the  grain. 

3.  Make  a  drawing  much  enlarged  to  show  the  shape  of 

one  of  the  roots  including  the  root-tip  and  the 
various  lengths  of  root-hairs.  Label  root-tip,  root- 
hairs. 

C.  Microscopical  structure  of  the  tip  of  a  root.     (Optional.) 

Examine  with  the  aid  of  the  low  power  of  the  compound  micro- 
scope a  root- tip  mounted  on  a  slide  in  drop  of  water  and  covered 
with  a  cover  glass.  Make  a  sketch  very  much  enlarged  to 
show  — 


THE  NUTRITIVE  ORGANS   OF  PLANTS  41 

1.  The  outline  of  the  root  including  the  tip. 

2.  A  loose  mass  of  cells  covering  the  lower  end  of  the  root  which 

make  up  the  roof-cap. 

3.  Label  root- tip,  cells  of  the  root- cap. 

56.    The  functions  of  roots.  —  Laboratory  Study  No.  30. 

A.  Roots  as  organs  for  holding  the  plant  to  the  soil. 

Secure  a  vigorously  growing  plant  in  a  pot  (e.g.  a  rubber 
plant)  or  better  try  the  following  experiment  on  a 
good  sized  weed  in  a  field.  Attach  to  the  stem  just 
above  ground  level  a  spring  balance.  Pull  on  the 
balance  until  the  plant  shows  signs  of  letting  go  its 
hold  on  the  soil,  then  note  the  reading  in  pounds  on 
the  scale. 

1.  In  your  own  words  describe  what  was  done. 

2.  How   much   force    in   pounds   was   exerted   on   the 

plant? 

3.  What  important  function  of  roots  is  shown  by  this 

experiment  ? 

B.  Roots  as  organs  for  absorbing  soil-water. 

(Before  proceeding  further  with  the  .root  study,  the  osmo- 
sis experiments,  44-53,  should  be  performed  if  they 
have  not  already  been  done.) 

Study  the  diagram  of  a  root-hair  in  the  text-book  (Fig.  12) 
and  if  possible  examine  with  the  low  power  of  the 
microscope  some  of  the  younger  (shorter)  root- 
hairs.  Each  root-hair  is  an  elongated  part  of  an 
outer  cell  of  the  root. 

1.  Draw  in  your  note-book  a  diagram  of  a  root-hair, 

labeling  cell-wall,  thin  layer  of  protoplasm,  cell- 
sap,  and  nucleus. 

2.  What   separates   the    soil-water   from  the   cell-con- 

tents? 

3.  Recall   the    characteristics   of   cellular   structure   as 

given  in  42.     Now  state  which  is  the  more  dense,  the 
soil-water  or  the  cell-contents. 


42  PLANT  BIOLOGY 

4.  In  which  direction,  therefore,  will  there  be  the  greater 

movement  of  liquid  in  the  process  of  osmosis  ? 

5.  How,  then,  is  a  root-hair  adapted  by  structure  for 

absorbing  soil-water? 

C.  Roots  as  organs  for  transmitting  soil-water. 

Place  some  seedlings  or  weeds  in  red  ink  so  that  only  the 
lower  ends  of  the  roots  are  in  the  liquid.  Cut  some 
cross  sections  of  these  roots  above  the  point  where 
they  were  in  contact  with  the  ink.  Examine  the 
cross  section  of  the  root  prepared  in  this  way. 

1.  Describe  the  experiment  as  it  was  performed. 

2.  Through  what  part  of  the  root   (cortex  or  central 

cylinder)  has  most  of  the  liquid  passed  ?  How  do 
you  know? 

3.  Make  a  sketch  about  an  inch  in  diameter  of  the  cross 

section  of  the  root,  to  show  the  colored  and  colorless 
portions.  Label :  part  of  the  root  through  which 
liquid  traveled,  unstained  portion  of  root,  cortex, 
central  cylinder. 

D.  Roots  as  organs  for  the  storage  of  food. 

Cut  some  slices  about  an  inch  thick  from  parsnips  or  other 
fleshy  roots,  and  divide  each  slice  vertically  in 
halves.  Put  the  pieces  in  water  and  boil  for  a  few 
moments  to  partially  cook  them.  Pour  iodine 
solution  over  some  of  the  pieces;  to  others  add 
strong  nitric  acid ;  boil  still  other  pieces  in  a  test 
tube  with  Fehling's  solution. 

1.  Describe  the  preparation  of  each  of  the  experiments, 

and  state  in  each  case  your  observations. 

2.  What  do  you  conclude  as  to  the  presence  or  absence  of 

each  of  three  of  the  food  substances  in  various  parts 
of  the  fleshy  root  you  are  studying? 

3.  What  function  of  roots  do  these  experiments  demon- 

strate? 

57.    Adaptations  of  roots  for  holding  to  the  soil.  —  One 

of  the  most  obvious  functions  of  roots  is  that  of  holding  plants 
firmly  in  the  ground.     If  the  soil  is  carefully  removed  from 


THE  NUTRITIVE  ORGANS   OF  PLANTS 


43 


the  roots  of  a  weed  or  a  tree,  these  roots  will  be  found  to 
extend  outward  in  all  directions  to  a  distance  even  greater 
than  do  the  branches  above  ground.  When  one  remembers 
the  tremendous  force  exerted  upon  trees  by  high  winds,  the 
necessity  for  this  extensive  root  anchorage  will  be  evident. 
In  our  dissection  of  the  root  even  of  a  young  plant  we  found 


FIG.  10.  —  Roots  of  a  tree,  showing  method  of  transplanting  a  large  tree. 
(Courtesy  of  Isaac  Hicks  and  Sons,  Westbury,  Long  Island.) 

that  the  central  cylinder  was  composed  of  tough  fibers  which 
are  made  up  of  elongated  wood-cells  (similar  to  those  shown 
in  Fig.  15).  As  a  plant  grows  older,  these  central  cylinders 
become  so  thick  and  tough  that  they  will  resist  an  enormous 
strain  without  breaking. 

58.  Adaptations  of  roots  for  absorbing  and  transmitting 
soil-water.  —  A  second  function  of  roots  we  found  to  be  that 
of  absorbing  soil-water  and  transmitting  it  to  the  stem.  The 


44 


PLANT  BIOLOGY 


whole  outer  surface  of  young  roots  is  covered  with  a  single 
layer  of  thin-walled  cells  which  form  the  epidermis.  Many  of 
these  cells  develop  tubular  outgrowths  known  as  root-hairs 


FIG.  11.  —  Cross  section  of  root, 
showing  root-hairs  and  epidermis 
cells  on  the  outer  surface,  cells  of 
cortex  within,  and  woody  central 
cylinder  with  its  ducts.  —  (Bailey.) 


FIG.  12.  —  Diagram  of  a  lengthwise 
section  of  two  root-hairs  with 
adjacent  cells  of  the  epidermis, 
and  with  two  cells  of  the  cortex. 


(see  56,  B).  By  studying  Fig.  12  it  will  be  evident  that  each 
root-hair  consists  of  a  cell-wall  lined  by  a  thin  layer  of 
protoplasm.  The  interior  of  the  cell  is  largely  filled  with 

cell-sap.  On  the  outside 
of  each  root-hair  is  soil- 
water.  All  the  conditions 
necessary  for  osmosis  are 

FIG.  13.  —  Portion  of  a  root-hair  with  ad- 
hering particles  of  soil.  —  (Strasburger.) 

which  separates  the  soil-water  from  the  denser  cell-sap. 
From  the  law  .of  osmosis,  we  should  expect  a  flow  of  liquids 
in  both  directions,  the  greater  flow  being  into  the  cell-sap 
from  the  soil-water.  It  has  been  found,  however,  that  the 


therefore    present.     The 
cell-wall  is  the  membrane 


THE  NUTRITIVE  ORGANS  OF  PLANTS 


45 


protoplasm  permits  the  inward  flow 
of  the  soil-water,  but  practically 
prevents  the  outward  flow  of  the 
cell-sap.  Thus  we  see  that  proto- 
plasm has  a  selective  action.  Since 
the  growing  parts  of  roots  have 
countless  root-hairs,  these  cells  of 
the  epidermis  together  act  like  a 
great  sponge  which  absorbs  the  large 
quantities  of  water  and  mineral  mat- 
ters which  are  needed  by  all  plants. 
This  liquid  passes  from  one  cell  to 
another  until  it  reaches  the  central 
cylinder.  A  study  of  the  micro- 
scopical structure  of  the  central  cyl- 
inder makes  evident  the  fact  that 
this  part  of  the  root  consists  not 
only  of  tough  wood  cells  as  explained 
in  the  preceding  section,  but  also  of  tubular  cells  called  ducts. 
(See  Fig.  14.)  Through  these  ducts  the  sap  is  conveyed  up- 
ward to  the  stem. 


FIG.  14. —  Ducts  that  convey 
the  sap  upward  through 
the  root,  stems,  and  leaf. 
The  walls  of  these  ducts 
are  strengthened  by  spiral 
fibers  or  rings. 


II.   THE  STRUCTURE  AND  ADAPTATIONS  OF  STEMS 

59.    The  structure  of  a  woody  stem.  —  Laboratory  Study 
No.  31. 

A.    The  structure  of  a  young  stem. 

Secure  pieces  of  a  young  stem  of  a  horse-chestnut,  maple, 
lilac,  or  other  woody  stem  that  shows  the  three 
layers  of  bark.  Split  some  pieces  lengthwise  in 
halves. 

1.  Peel  off  the  outer  covering,  the  bark,  from  a  piece  of 
the  stem  till  the  wood  is  exposed.  The  bark  of 


46  PLANT  BIOLOGY 

a  young  stem  usually  consists  of  three  more  or 
less  distinct  layers. 

a.  With  a  knife  gently  scrape  off  an  outer  or  brown 

bark,  and  expose  a  dark  green  layer  known  as  the 
green  bark.  Scrape  this  until  you  come  to  a 
more  or  less  tough  layer  known  as  the  fibrous 
bark  or  bast  (which  may  be  slightly  green). 
Describe  each  of  these  barks  as  to  position  and 
color. 

b.  Pick  into  threads  the  fibrous  bark ;  in  what  direc- 

tion of  the  stem  do  the  fibers  run?  By  break- 
ing strips  of  each  layer  determine  which  of  the 
three  barks  is  toughest. 

2.  Feel  of  the  wood  from  which  the  bark  has  just  been 

removed.  Describe  the  substance  which  covers 
the  wood,  after  scraping  off  a  little  with  your 
thumb  nail.  This  is  the  cambium  or  growing 
layer,  which  produces  the  new  wood  and  bark. 
When  the  bark  is  torn  off,  the  cells  of  this  layer 
are  broken  and  the  slimy  protoplasm  oozes  out. 

3.  By  means  of  a  penknife  or  pin  dig  into  the  wood  and 

also  into  the  pith  at  the  center  of  the  stem. 
Compare  the  wood  and  the  pith  as  to  relative 
position  and  hardness. 

4.  By  the  aid  of  compasses  make  a  diagram,  at  least  three 

inches  in  diameter,  of  the  cross  section  of  a 
woody  stem  to  show  the  relative  thickness  of 
the  various  layers.  (These  layers  might  well  be 
represented  by  different  colors.)  Label  brown 
bark,  green  bark,  fibrous  bark  or  bast,  cambium 
layer,  wood,  pith. 

B.    The  structure  of  an  older  stem.     (Optional.) 

Cut  some  cross  sections  of  stems  several  years  old.  (Ad- 
mirable material  can  be  obtained  by  sawing  into  pieces 
about  two  inches  long  white  oak  sticks  three  to  four 
inches  in  diameter.)  Each  piece  should  then  be  split 
into  halves  and  each  surface  planed  and  sandpapered. 
These  pieces  are  valuable  as  permanent  preparations. 


THE  NUTEITIVE  ORGANS   OF  PLANTS  47 

1.  Which  of  the  three  regions  (bark,  wood,  and  pith)  found  in 

the  young  stem  can  you  readily  distinguish  ?  Which 
of  the  three  becomes  very  much  thicker  and  harder  as 
the  stem  grows  older  ?  Which  is  very  small  in  quan- 
tity when  compared  with  the  young  stem  ? 

2.  The  curved  layers  of  wood  hi  the  cross  section  are  known  as 

annual  rings,  so  called  because  usually  only  one  ring  is 
formed  each  year  by  the  cambium  layer.  How  many 
years  of  growth  are  shown  in  the  piece  of  wood  you 
are  studying  ? 

3.  The  lines  hi  the  cross  section  extending  like  the  spokes  of  a 

wheel  are  the  pith  rays  or  medullary  rays.  Describe 
the  appearance  of  these  rays.  The  shining,  lighter 
colored  surfaces  (to  which  the  beauty  of  "quartered 
oak"  furniture  is  due),  that  appear  hi  the  longitudinal 
sections  of  oak  wood,  are  the  pith  rays.  Find  pith 
rays  in  the  middle  surfaces  of  some  of  the  oak  pieces 
you  are  studying,  and  describe  them. 

4.  Make  a  large  diagram  of  the  cross  section  of  the  piece  of 

wood  you  are  studying.  Label  bark,  wood,  annual 
rings,  medullary  or  pith  rays. 

60.  The  structure  of  the  com  stem.  —  Laboratory  Study 
No.  32.  (Optional.) 

Cut  pieces  about  two  inches  in  length  from  full-grown  corn  stalks,  and 
split  each  piece  in  halves.  (If  necessary  these  pieces  may  be  preserved 
from  year  to  year  in  4  per  cent  formalin  or  in  70  per  cent  alcohol.) 

Examine  the  cross  and  longitudinal  sections  of  corn  stem.  Find 
the  rind  (the  outer  layer),  the  woody  bundles  or  fibers  (thread-like 
structures),  and  the  pith  (material  between  the  bundles). 

1.  Thrust  your  pencil  point  into  the  pith;  is  this  material  hard  or 

soft? 

2.  Pull  out  one  of  the  woody  fibers ;  is  it  tough  or  tender  ? 

3.  Push  your  pencil  point  into  the  rind ;  is  it  hard  or  soft  ? 

4.  Make  a  drawing   (X  2)   showing  both  cross  and  longitudinal 

surfaces.     Label  rind,  woody  bundles,  pith. 


48  PLANT  BIOLOGY 

61.  Experiments  to  show  the  upward  path  of  sap  through 
stems.  —  Laboratory  Study  No.  33. 

A.  Stand   some  live  twigs  (e.g.  maple  or  horse-chestnut)  in 

red  ink  for  a  day  or  two ;  cut  off  pieces  above  the 
level  of  the  ink,  and  split  some  of  these  pieces  in 
half  lengthwise. 

1.  Describe  the  preparation  of  the  experiment. 

2.  Through  what  part  of  the  stem  does  the  red  ink  rise  ? 

3.  What  do  you  conclude,  therefore,  as  to  the  part  of  a 

woody  stem  through  which  sap  rises? 

B.  (Optional.)     Stand  in  red  ink  some  pieces  of  fresh  corn  stalk 

(or  if  this  cannot  be  obtained,  some  Tradescantia  or 
any  lily  stem).  Cut  some  cross  and  longitudinal  sec- 
tions above  the  level  of  the  ink. 

1.  Write  an  account  of  the  experiment,  stating  your  observations. 

2.  In  the  stem  you  are  studying,  is  sap  carried  upward  by  the 

rind  (epidermis  in  the  lily),  or  by  the  pith,  or  by  the 
woody  fibers  ?  How  do  you  know  ? 

62.  Stems  as  organs  for  support  and  leaf  exposure.  — 

When  we  studied  the  manufacture  of  carbohydrates  by  plants, 
we  proved  that  green  leaves  must  be  exposed  to  sunlight  in 
orcfer  to  carry  on  this  important  function.  When  the  leaves 
receive  the  proper  amount  of  exposure,  the  food  can  be 
manufactured  rapidly.  Hence,  we  should  expect  to  find  that 
leaves  are  arranged  in  such  a  way  as  to  secure  the  best 
amount  of  sunlight.  Where  plants  are  more  or  less  crowded, 
as  in  forests  or  thickets,  the  main  stems,  such  as  the  trunks  of 
trees,  usually  grow  tall,  thus  lifting  the  leaves  to  the  light. 
The  amount  of  light  exposure  of  trees  and  of  most  other  plants 
is  largely  increased  by  branches  and  their  subdividing  twigs, 
to  which  the  leaves  are  attached. 

In  order  that  the  trunk  and  its  branches  may  be  able  to 
support  the  leaves  and  withstand  the  force  of  storms,  thick- 


THE  NUTRITIVE  ORGANS   OF  PLANTS 


49 


walled  wood-cells  are  developed.  Each  wood-cell,  when 
separated  out  from  the  rest,  and  examined  with  the  high 
power  of  the  compound  microscope,  is  seen  to  be  shaped 
somewhat  like  a  tiny  toothpick,  and  the  thin  ends  of  these 
cells  fit  together  closely  by  overlapping.  (See  Fig.  15.) 


bast 
cells 


sieve  tube 


duct 


duct 


FIG.  15.  — Woody  bundle  of  sunflower  stem. 

Stems  like  the  corn  stalk  and  bamboo  have  most  of  their  sup- 
porting material  on  the  outside,  and  these  stems  are  in  the  form  of 
cylinders  which  are  either  hollow  (as  in  grasses)  or  filled  with  pith 
through  which  pass  the  woody  bundles  (as  in  the  corn  stalk).  It 
has  been  proved  that  when  a  given  amount  of  material  is  arranged 
in  the  form  of  a  hollow  tube,  it  will  withstand  a  much  greater  strain 
without  breaking  than  when  this  material  is  in  the  form  of  a  solid 
rod.  This  mechanical  principle  is  made  use  of  in  the  construction 
of  the  frame  of  a  bicycle  and  of  the  pillars  that  support  buildings. 

63.  Stems  as  organs  for  the  transmission  of  sap.  —  Leaves 
not  only  require  an  abundance  of  sunlight,  but  they  must 


50 


PLANT  BIOLOGY 


also  be  supplied  with  water  and  other  materials  from  the 
soil.  Our  experiment  with  red  ink  (see  61)  showed  that  the 
soil-water  is  carried  upward  through  the  woody  portions  of 
stems.  A  microscopical  examination  of  thin  sections  of 
a  stem  (see  Fig.  15)  shows  the  presence  of  tubular  cells 
known  as  ducts,  similar  to  those  found  in 
the  central  cylinder  of  roots  with  which 
they  are  connected.  These  are  the 
parts  of  the  wood  through  which  the 
soil-water  passes  most  readily  up  to  the 
leaves. 

After  the  raw  materials  have  been 
changed  into  the  plant  foods  by  green 
leaves,  these  plant  foods,  by  the  process 
of  digestion,  are  changed  into  such  a 
form  that  they  can  pass  from  the  leaves 
into  the  fibrous  bark  in  which  are  tubular 
cells  known  as  sieve-tubes.  (See  Figs.  15 
and  16.)  Through  these  the  liquid  food 
passes  down  the  stem  to  be  stored  away 
or  used  in  the  growth  of  root  or  stem. 
In  young  stems  the  pith  rays  or  medul- 
lary rays  (59,  B,  3),  the  fine  lines  extend- 
ing from  the  bark  toward  the  center  of 
the  stem,  are  supposed  to  serve  as  chan- 
nels for  the  passage  of  food  across  the 
stem  and  also  for  the  storage  of  food. 


B 


FIG.  16. —  Sieve  tube, 
that  conveys  sap 
downward  through 
the  leaf,  stem,  and 
root.  A,  longitu- 
dinal section  show- 
ing edge  view  of 
sieve  plate  (in  the 
middle)  ;  B,  sur- 
face view  of  sieve 
plate. 


In  the  type  of  stem  represented  in  the  corn,  lilies,  and  palm 
trees,  the  woody  material  through  which  sap  passes  is  not  ar- 
ranged in  the  form  of  annual  rings,  but  the  woody  bundles  are 
scattered  through  the  pith.  Each  bundle  consists  of  ducts  that 
carry  the  soil-water  up  through  the  stem  out  into  the  leaves,  of 
sieve-tubes  that  convey  downward  from  the  leaves  the  manufac- 


THE  NUTRITIVE  ORGANS  OF  PLANTS 


51 


tured  food  substances,  and  of  wood  .cells  that  help  to  strengthen  the 
bundle. 

64.  Changes  in  stems  during  their  growth.  —  In  our  dis- 
cussion thus  far,  we  have  considered  the  adaptations  of  stems 
for  exposing  leaves  to  the  light  and  for  transmitting  food 
materials  to  and  from  the  leaves.  But  the  stem  has  other 
important  functions  which  we  are  now  to  consider.  In  a 
young  twig,  before  the  brown  bark  thickens  and  shuts  out 
the  light,  the  green  bark,  on  account  of  the  presence  of  chlo- 
rophyll, is  enabled  to  carry  on  the  manufacture  of  carbohy- 
drates. In  a  very  young  stem  the  surface  is  covered  by  thin 
epidermis  which  helps  to  prevent 
the  undue  escape  of  moisture.  In 
this  layer  are  tiny  openings  that 
allow  the  inward  and  outward 
passage  of  gases  that  occur  in 
breathing  and  food  manufacture. 
Later  this  epidermis  is  replaced 
by  the  outer  or  brown  bark,  which 
serves  as  a  means  of  protection 
against  unfavorable  weather  con- 
ditions and  insects.  In  this  brown 
bark  the  tiny  openings  referred 
to  above  are  developed  into  large 
openings  known  as  lenticels  which 
carry  on  the  same  functions.  In  an  old  tree  the  outer  bark 
becomes  very  thick  and  corky  and  the  green  layer  dis- 
appears entirely. 

The  growth  of  the  tree  in  thickness,  as  already  stated,  is 
due  to  the  activity  of  a  layer  of  cells  between  the  wood  and  the 
fibrous  bark.  This  is  the  cambium  layer  (Fig.  15).  In  early 
spring  the  cambium  cells  by  rapid  growth  and  division  form 
on  their  innermost  surface  a  new  layer  of  wood  (which  appears 


FIG.  17. —  Cross  section  of  a 
tree  trunk  showing  bark, 
wood  (with  its  annual  rings 
and  medullary  rays),  and  pith 
at  center.  —  (Courtesy  of 
New  York  Botanical  Garden.) 


52 


PLANT  BIOLOGY 


FIG.  18.  —  Cross  section  of 
young  bamboo,  showing  hard 
outer  rind,  woody  bundles, 
scattered  through  the  pith. 
The  center  of  the  stem  is 
hollow.  —  (Courtesy  of  New 
York  Botanical  Garden.) 


as  a  ring  in  cross  section),  and 
on  their  outer  surface  more  fibrous 
bark.  As  the  season  advances, 
the  activity  of  these  cells  becomes 
less  and  less,  and  finally  growth 
ceases  during  the  winter.1 

Stems  of  plants  like  the  corn,  bam- 
boo, and  palm  have  no  true  cambium 
layer,  and  therefore  even  in  the  case 
of  plants  of  this  type  that  live  on 
from  year  to  year  no  annual  rings  are 
formed.  In  the  growth  of  these  stems, 
new  bundles  develop  in  the  pith  be- 
tween thqse  already  formed. 


III.     THE  STRUCTURE  AND  ADAPTATIONS  OF  LEAVES 

65.  Leaf  arrangement.2  —  Along  the   sides  of  twigs  leaves  are 
arranged  in  such  a  way  as  to  secure  as  much  light  as  possible  with- 
out being  shaded  by  the  leaves  above  them.     Thus  in  plants  like 
the  horse-chestnut,  maple,  and  lilac,  the  leaves  are  arranged  so  that 
at  a  given  level  on  the  twig  two  leaves  are  opposite  each  other, 
while  the  next  pair  are  at  right  angles  to  the  first  pair.     This  is 
known  as  an  opposite  arrangement.     The  beech,  elm,  and  rose,  on 
the  other  hand,  have  an  alternate  arrangement,  only  one  leaf  being 
found  at  a  given  level  on  the  twig. 

66.  External  structure  of  a  horse-chestnut   twig.  —  Laboratory 
Study  No.  34.  —  (Optional.)     (Maple,  beech,  or  other  woody  twig 
may  be  used  with  slight  verbal  changes.) 

1  Sometimes  trees  form  more  than  one  ring  during  a  season. 

2  Before  assigning  this  section  for  study,  the  teacher  should  dem- 
onstrate from  leafy  twigs  (e.g.   maple,  horse-chestnut,  lilac,  elm, 
apple)    the    characteristic    differences   between   the   opposite   and 
alternate  arrangement  of  leaves. 


THE  NUTRITIVE   ORGANS   OF  PLANTS 


53 


A.  Leaf  scars.     (The  horseshoe-shaped  scars  with  the  raised  dots 

like  horseshoe  nails  indicate  the  places  where  the  stalks 
of  the  leaves  were  attached.) 

1.  Do  the  leaf  scars  occur  in  pairs,  or  is  there  only  one  scar 

at  a  given  level?    How,  therefore,   were  the  leaves   ar- 

ranged on  the 

stem? 

2.  Count  the  num- 

ber of  dots  on 
several  differ- 
ent leaf  scars  ; 
these  dots  are 
the  ends  of 
the  wood 
bundles  that 
carried  sap  to 
the  various 
leaflets.  Look 
at  the  picture 
ofhorse-chest- 
nut  leaves. 
(See  Fig.  20, 
K)  How 
many  main 
veins  do  you 
find  in  one 

compound     FlG-  19-  —  sPray 
ifn      f^ 

pare    this 

number  with  the  number  of  dots  on  the  leaf  scars  ;  what 
.  •      do  you  conclude  ? 

B.  Buds.     (At  the  end  of  most  twigs  is  a  single  terminal   bud; 

the   buds   along  the   side   of   the  twig  are   lateral   buds. 
Each  bud  is  covered  with  bud-scales.) 

1.  State  the  position  of  each  kind  of  bud  on  the  twig.     Where 
are  the  lateral  buds  found  with  reference  to  the  leaf  scars  ? 


young  apple  tree,  showing 
alternate  arrangement.  At  the  base  of  each 
leaf  stalk  is  a  pair  of  small  stipules.  —  (Bailey.) 


FIG.  20.  —  Forms  of  leaves.  —  (Courtesy  of  Furman  and  Miller,  Botanical  Aid, 
Western  Publishing  Co.,  Chicago,  111.) 


A,  lilac; 

B,  chestnut ; 


E,  locust ; 

K,  horse-chestnut ; 


7,  sweet  gum ; 
J,  buttercup ; 


Simple  leaves 

C,  white  oak ;  G,  oak  ; 

D,  celandine ;  H,  geranium ; 

Compound  leaves 

L,  cinquefoil ;  F,  wild  tamarind 

M,  wild  strawberry  ;  (twice  compound). 

54 


THE  NUTRITIVE  ORGANS  OF  PLANTS  55 

2.  Look  carefully  at  the  scales  of  the  terminal  bud  to  see  if  they 

have  any  definite  arrangement.  State  whether  or  not  this 
arrangement  corresponds  to  that  of  the  leaf  scars. 

3.  (Demonstration.)     Examine  a  terminal  bud  from  which  one 

or  two  scales  have  been  removed.  Bud-scales  are  modified 
leaves.  How  do  these  scales  differ  from  ordinary  leaves  ? 
What  is  the  use  of  the  scales  to  the  bud  ?  How  are  they 
adapted  for  this  use  ? 

C.  Bud-scale  scars.     (These  are  also  called  annual  scars  because 

they  are  formed  at  the  beginning  of  the  growing  season  of 
each  year  when  the  terminal  bud  opens  and  its  scales  fall 
off.  To  prove  this,  remove  one  or  two  outside  scales  from 
a  terminal  bud,  and  note  the  scar  thus  formed.) 

1.  How  many  groups  of  bud-scale  scars  or  annual  scars  do  you 

find  on  the  twig  you  are  studying  ? 

2.  Since  one  set  is  formed  each  spring,  how  many  years  of 

growth  are  shown  on  the  twig  ? 

D.  Breathing  pores  or  lenticels.     Look  for  small  elevations  on  the 

bark.    These  locate  the  lenticels.     Describe  the  lenticels. 

E.  Make  a  careful  outline  drawing  of  the  twig,  showing  its  form, 

the  position  and  shape  of  the  leaf  scars  with  their  woody 
bundles,  the  terminal  and  lateral  buds,  bud-scales,  bud- 
scale  scars,  and  lenticels.  Label  each  of  the  structures 
shown  in  your  drawing. 

67.    The  structure  of  leaves.  —  Laboratory  Study  No.  35. 
A.    Parts  of  a  leaf. 

1.  Examine  a  simple  leaf,  e.g.  maple,  geranium,  or  lilac, 
and  note  that  it  is  made  up  of  the  following 
parts :  a  leaf-stalk,  which  attaches  the  main  part 
of  the  leaf  to  the  stem  of  the  plant,  and  the 
blade,  the  flat,  expanded  portion. 

a.  How  does  the  blade  differ  in  form  from  the  leaf- 
stalk? 

6.  Hold  the  leaf  to  the  light.  How  many  main  veins 
do  you  find?  Where  are  they  smallest?  By 
what  are  the  main  veins  connected  ? 


56  PLANT  BIOLOGY 

c.  Make  a  drawing,  natural  size,  by  tracing  the  out- 
line of  the  leaf-stalk  and  blade.  Draw  carefully 
the  principal  veins  and  a  few  of  their  branches, 
being  careful  to  show  their  relative  size  and  their 
connections.  Label  leaf -stalk,  blade,  main  veins, 
network  of  veins. 

2.  (Optional.)  Examine  a  compound  leaf,  e.g.  rose,  clover, 
locust,  pea,  horse-chestnut.  Notice  that  the  blade  is 
divided  into  three  or  more  parts  known  as  leaflets, 
which  are  attached  either  to  the  end  of  the  leaf- 
stalk or  on  either  side  of  the  mid-vein  of  the  com- 
pound leaf. 

a.  In  what  respect,  therefore,  does  the  blade  of  a  com- 
pound leaf  differ  from  the  blade  of  a  simple  leaf  ? 

6.  Compare  the  arrangement  of  the  leaflets  in  a  leaf  like 
the  rose,  locust,  or  pea  with  that  in  the  Virginia 
creeper  or  horse-chestnut.  Which  leaves  have  the 
leaflets  arranged  like  the  bones  in  the  palm  of  the 
hand  (palmately  compound),  and  which  have  the 
leaflets  arranged  along  the  side  of  the  mid- vein  as  in 
a  feather  (pinnately  compound,  from  Latin,  pinna  = 
feather)  ? 

c.  At  the  base  of  the  leaf-stalk  of  the  rose,  clover,  or  pea  leaf, 
notice  two  leaf-like  objects  (small  in  the  case  of  the 
rose).  These  are  known  as  stipules.  Stipules  are  also 
found  as  a  part  of  many  simple  leaves.  How  do 
stipules  differ  from  the  other  parts  of  leaves  ?  (See 
Fig.  19.) 

B»  Gross  structure  of  leaves.  —  Secure  thick  leaves  such  as 
sedum,  tulip,  hyacinth,  or  onion. 

1.  Peel  off  from  the  upper  and  lower  surface  a  thin 
membrane  known  as  the  epidermis.  Hold  the 
epidermis  between  yourself  and  the  light.  Tell 
what  you  have  done  and  state  two  characteristics 
of  epidermis. 


THE  NUTRITIVE  ORGANS  OF  PLANTS  57 

2.  Examine  the  material  left  after  removing  the  epi- 

dermis, scraping  it  with  a  knife.  This  inner 
region  of  the  leaf  is  known  as  mesophyll  (Greek, 
meso  =  middle  -j-  phullon  =  leaf).  Describe  the 
mesophyll,  stating  how  it  differs  from  the  epi- 
dermis. 

3.  Look  carefully  for  veins  in  the  mesophyll.     Describe 

their  appearance. 

4.  (Optional.)     Make  a  diagram  at  least  half  an  inch  in  thick- 

ness of  a  small  portion  of  the  cross  section  of  the  leaf 
you  are  studying,  labeling  upper  epidermis,  mesophyll, 
veins,  and  lower  epidermis. 

C.   Microscopical  structure  of  leaves.  —  Demonstration. 

1.  Strip  off  a  piece  of  epidermis  from  one  of  the  thick 
leaves  named  in  B  above ;  lay  it  on  a  glass  slide, 
add  a  drop  of  water,  and  cover  with  a  cover  glass. 
Examine  with  the  low  power  of  the  compound 
microscope,  comparing  the  specimen  with  Fig. 
21.  Notice  the  shape  of  the  cells  of  which  the 


guard-cells  sur- 
rounding   a 


cells  of  epider- 
mis 


FIG.  21.  —  Lower  epidermis  of  a  leaf.  —  (Strasburger.) 

epidermis  (shown  by  the  faint  outlines  of  their 
walls)  is  composed.  -Find  little  oval  bodies  scat- 
tered among  the  cells  of  the  epidermis,  each  hav- 


58 


PLANT  BIOLOGY 


ing  an  opening  in  the  middle.  This  opening  is 
called  a  stoma,  plural  stomata  (Greek,  stoma  = 
mouth).  Each  stoma  is  surrounded  by  two 
guard-cells. 

Make  a  diagram,  greatly  enlarged,  of  a  stoma  with  its 
guard-cells,  together  with  the  cells  of  the  epi- 
dermis that  immediately  surround  it.  Label 
cells  of  the  epidermis,  guard-cells,  stoma. 


upper  epidermis 


chlorophyll  bodies  N~~ 


air  space 


/  mesophyll  cells  con- 
/          taining      chloro- 
phyll bodies 


lower  epidermis 


stoma  with  a  guard-cell  on  either  side 
FIG.  22. —  Cross  section  of  a  leaf.  —  (Strasburger.) 

2.  Study  Fig.  22  and  make  out  the  shape  and  location  of 
each  of  the  following  parts  of  which  it  is  com- 
posed :  upper  epidermis,  mesophyll  cells,  chloro- 
phyll bodies,  air  spaces  between  the  cells,  lower 
epidermis,  stoma.  In  your  note -book  make  a 
drawing  considerably  enlarged  showing  a  small 
portion  of  the  cross  section,  and  label  each  part. 

68.    Experiment  to  demonstrate  the  path  of  sap   through 
leaves.  —  Laboratory  Study  No.  36. 

Place  in  red  ink  the  lower  end  of  a  leafy  branch  of  any 
vigorous  plant,  e.g.  geranium  or  bean   seedling,   and  allow 


THE  NUTRITIVE  ORGANS   OF  PLANTS 


59 


it  to  stand  in  sunlight  or  a  warm  place  until  the  red  color 
appears  in  the  leaves. 

1.  Give  an  account  of  the  experiment,  stating  your  observa- 

tions. 

2.  What  do  you  conclude  as  to  the  part  of  the  leaf  through 

which  soil -water  is  distributed  to  different  parts  of  the 
blade? 

3.  What  cells  of  the  root  did  you  find  specially  adapted  for 

absorbing  water  from  the  soil  ?     Through  what  regions 
of  the  root  and  stem  is  sap  carried  up  to  the  leaves? 

69.    Is  water  vapor  given  off  by  the  leaves  of  a  green  plant? 
—  Laboratory  Study  No.  37.     Demonstration. 

1.  Wrap  sheet  rubber  or  thin  oilcloth  about  a  pot  containing 
a  vigorous  plant  which  has  been  thoroughly  watered. 
Tie  the  rubber  or  oilcloth  tightly  about  the  stem  to 
prevent  the  escape  of 
water  from  the  soil.  If 
rubber  tissue  cannot  be 
obtained,  melted  paraffin 
may  be  poured  over  the 
soil,  and  the  pot  painted 
with  hot  paraffin.  Cover 
the  plant  thus  prepared 
with  a  large  bell  jar  with 
the  inner  surface  dry,  and 
stand  it  in  the  sun  for  a 
few  hours. 

a.  Describe  the  preparation  of 

the    experiment,    stating 
the  reason  for  using  the 
^  rubber  or  paraffin. 

b.  State  your  observations  and 

conclusion. 

c.  Why  is  the  bell  jar  necessary? 

d.  What  becomes  of  the  water 

Vapor    given    off    by    the    FIG.  23. -Apparatus  to  show  the 
leaves  OI  trees:  excretion  of  water  from  a  plant. 


60  PLANT  BIOLOGY 

2.  (Optional.)  Put  the  plant  prepared  as  above  on  one  of  the 
scale  pans  of  a  balance  and  with  it  a  stoppered  graduate 
or  a  stoppered  bottle.  On  the  other  pan  put  weights 
enough  to  equalize  the  balance.  At  the  end  of  24 
hours  put  enough  water  into  the  graduate  or  bottle  to 
cause  the  weights  on  the  two  pans  to  be  equal. 

a.  Describe  the  preparation  of  the  experiment. 

6.  What  volume  of  water  was  necessary  to  equalize  the  weights 
(i.e.  how  much  water  was  given  off  from  the  plant  in 
24  hours)  ? 

c.  In  a  similar  way  add  water  each  24  hours  for  a  week  or 

until  the  plant  shows  signs  of  wilting.  What  is  the  total 
amount  of  water  given  off  during  the  experiment  ? 

d.  Bearing  in  mind  the  relative  amount  of  leaf  surface  of  this 

plant  and  on  the  trees  of  a  forest  of  even  a  few  acres, 
what  would  you  infer  as  to  the  quantity  of  water  given 
off  by  the  trees  of  a  forest  during  a  summer  season  ? 

70.  Leaves  as  organs  for  food  manufacture.  —  While 
studying  the  manufacture  by  plants  of  carbohydrates  (sugar 
and  starch)  we  showed  that  the  raw  materials  necessary  for 
this  process  are  water  and  carbon  dioxid.  We  have  proved 
that  water  enters  the  root-hairs  by  osmosis  and  travels  in  a 
system  of  ducts  through  the  woody  portion  of  roots  and  stems 
out  to  the  leaves.  Here  the  ducts  of  the  stems  connect  with  a 
network  of  veins  containing  similar  ducts  by  means  of  which 
the  soil-water  is  supplied  to  the  cells  that  are  to  manufacture 
the  food.  The  carbon  dioxid  that  is  needed  is  secured  from 
the  air.  This  gas  passes  through  the  openings  (stomata) 
in  the  epidermis,  and  enters  the  air  spaces  in  the  mesophyll, 
and  finally  reaches  the  cells  containing  the  chlorophyll 
bodies. 

The  sunlight  acting  upon  the  chlorophyll  bodies  enables 
them  to  combine  the  elements  found  in  the  water  and  carbon 
dioxid  to  form  carbohydrates.  These,  as  we  have  seen,  are 


THE  NUTRITIVE  ORGANS   OF  PLANTS  61 

probably  used  in  the  manufacture  of  proteins.  In  the  leaves, 
as  elsewhere  in  the  plant,  the  various  foods  are  digested  and 
thus  are  prepared  to  be  carried  by  the  tubular  cells  (sieve 
tubes)  in  the  veins  and  down  through  similar  tubular  cells  in 
the  fibrous  bark.  (Fig.  16.) 

71.  Excretion  of  the  by-products  of  food  manufacture.  — 
We  showed  in  35  that  during  the  process  of  carbohydrate 
manufacture  oxygen  is  set  free,  and  this  gas  is  given  off 
through  the  stomata  into  the  air.     Water,  too,  is  a  by-prod- 
uct of  food  manufacture  and  assimilation.     In  the  manu- 
facture of  proteins  mineral  matters  are  necessary,  and  these 
are  carried  up  the  stem  dissolved  in  the  soil-water.     Since, 
however,  the  soil-water  is  such  a  dilute  solution,  great  quan- 
tities of  this  liquid  must  be  supplied ;  hence,  much  more  water 
is  taken  in  than  is  needed  for  food  manufacture  or  making  of 
protoplasm.     This  excess  of  water  is  given  off  in  large  quan- 
tity by  the  leaves  of  green  plants  (see  69). 

The  amount  of  water  thus  excreted  by  leaves  is  regulated 
more  or  less  by  the  action  of  the  guard-cells  that  surround  each 
stoma.  When  the  plant  is  well  supplied  with  water,  the  stoma 
remains  wide  open.  If,  on  the  other  hand,  the  leaves  lack  a 
sufficiency  of  water,  these  guard-cells  close  in  upon  the  stoma, 
and  so  prevent  undue  loss  of  moisture.  In  plants  having 
leaves  in  a  horizontal  position,  the  stomata  are  mostly  located 
on  the  lower  surface,  the  upper  surface,  which  is  more  exposed 
to  the  sunlight,  being  covered  with  a  continuous  layer  of 
epidermal  cells.  Were  the  epidermis  altogether  absent  from 
leaves,  the  mesophyll  cells  would  soon  lose  so  much  water 
that  they  would  die. 

72.  Storage    of   foods   in   plants.  —  The  foods    that   are 
manufactured  in  the  chlorophyll-bearing  cells  may  be  car- 
ried, as  we  have  seen,  to  other  parts  of  the  plant,  there  to  be 


62 


PLANT  BIOLOGY 


stored  until  needed.  Whenever  large  amounts  of  starch, 
sugar,  protein,  or  fat  are  thus  stored,  the  organs  containing 
these  substances  frequently  become  enlarged  (e.g.  carrot  (Fig. 
81),  potato  (Figs.  49,  60),  and  onion)  and  the  walls  of  the  cells 
in  these  organs  usually  remain  thin  and  soft,  permitting  the 
inward  and  outward  passage  of  food.  (See  Fig.  9.) 

73.    Summary  of  functions  of  the  parts  of  the  nutritive 
organs  of  green  plants. 


NAME  OF  PART 

WHERE  PART  is  FOUND 

PRINCIPAL  FUNCTION  OR  FUNCTIONS 
OF  PARTS 

Epidermis 

Covering  of  root 

Absorbs    soil-water,    largely 

through  root-hairs 

Epidermis 

Covering  of  stem 

Protects    inner  layers,    pre- 

and leaves 

vents     undue    escape    of 

moisture 

Lenticels 

Brown     bark     of 

Permit  entrance  of  0  and  CC>2 

stem 

and  escape  of  0  and  C02 

Stornata 

Epidermis           of 

Permit  entrance  of  0  and  C02 

leaves 

and  escape  of  0  and  CC>2 

Guard-cells 

Surround  stomata 

Regulate  escape  of  H20 

Air  spaces 

Between       meso- 

Serve  as  reservoirs  of  0  and 

phyll  cells 

C02  and  water  vapor 

Chlorophyll- 

Mesophyll           of 

Manufacture  carbohydrates 

bearing  cells 

leaves,        green 

bark  of  stem 

Ducts 

Central  cylinder  of 

Transport  soil-water  upward 

root,  woody  part 

through  the  plant 

of  stem,  veins  of 

leaves 

Sieve  tubes 

Fibrous    bark    of 

Transport      digested     foods 

stem,    veins    of 

downward  through  plants 

leaves 

THE  NUTRITIVE  ORGANS  OF  PLANTS 


63 


NAME  OF  PART 

WHERE  PART  is  FOUND 

PRINCIPAL  FUNCTION  OR  FUNCTIONS 
OF  PARTS 

Wood  cells 

Central  cylinder  of 

Resist  forces  tending  to  break 

root,  woody  part 

roots,  stems,  or  leaves 

of  stem,  veins  of 

leaves 

Cambium  layer 

Between  bark  and 

Provides  for  growth  of  wood 

wood  of  stem 

and  fibrous  bark  or  bast 

Pith 

Interior  of  stem 

Stores  food 

Pith-rays 

Woody    layer    of 

Transfer  food   across   stem, 

stem 

and  store  food 

CHAPTER   VI 

RESPIRATION   AND   THE  PRODUCTION   OF  ENERGY  IN 
PLANTS 

I.   THE  STORAGE  AND   LIBERATION   OF   ENERGY 

74.  Examples  of  energy  in  plants.  —  By  energy  we  mean 
the  capacity  to  do  work.     In  the  preceding  chapters  we 
have  considered  to  some  extent  the  structure  of  various  parts 
of  plants  and  some  of  the  functions  which  they  are  fitted  to 
perform.     Now  to  carry  on  most  of  these  functions  requires 
the  expenditure  of  energy  on  the  part  of  the  plant.     Thus, 
for  example,  roots  in  growing  expend  considerable  energy, 
pushing  their  way  through  the  soil.     Stems  in  like  manner 
exert  energy  in  lifting  to  the  light  and  air  their  weight  of 
branches   and   leaves.     We   know,  too,    that    soil-water   is 
carried  up  through  plants  to  considerable  heights  (several 
hundred  feet  in  very  large  trees),  that  substances  obtained 
from  the  soil  and  air  are  digested  and  transported  from  one 
part  of  a  plant  to  another.     Still  another  form  of  energy 
exhibited  to  a  certain  degree  by  plants  is  heat,  as  the  follow- 
ing experiment  will  show. 

75.  To  prove  that  heat  energy  is  developed  in  growing  seed- 
lings. —  Laboratory  Study  No.  38. 

Secure  two  wide-mouthed  bottles  of  the  same  size  (light- 
ning fruit  jars  will  answer)  and  put  some  wet  blotting  paper 
in  the  bottom  of  each.  Fill  one  of  the  jars  half  full  of  sprout- 
ing peas.  Fill  the  other  jar  half  full  of  peas  that  have  been 
killed  by  being  soaked  in  a  5  per  cent  solution  of  formalin  for 

64 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS          65 

twenty-four  hours.  Rinse  the  seeds  with  boiled  water  to 
remove  the  preserving  fluid.  Get  two  thermometers  that 
have  approximately  the  same  temperature  reading  in  the  air 
of  the  laboratory.1  Push  the  lower  end  of  the  thermometer 
down  among  the  sprouting  seeds  so  that  the  mercury  will  be 
covered  by  the  seeds.  Do  the  same  with  the  second  ther- 
mometer in  the  jar  of  dead  seeds.  Set  the  jars  side  by  side 
in  a  warm  place  for  twenty-four  hours  or  more. 

1.  Describe  the  preparation  of  this  experiment.     In  what 

respects  are  the  conditions  the  same  in  both  jars?  In 
what  one  respect  do  the  two  jars  differ? 

2.  Take  the  temperature  readings  of  the  thermometer  in  each 

of  the  two  jars  and  record  results.  What  difference 
do  you  notice  in  the  temperature  of  the  seeds  in  the  two 
jars? 

3.  What  is  your  conclusion  from  the  experiment  as  to  the 

development  of  heat  energy  in  seedlings? 

76.  Energy  and  its  transformations.  —  We  see  from  the 
preceding  discussion  and  experiment  that  plants  exhibit 
considerable  energy  or  ability  to  do  work.  Animals  and 
man,  however,  show  far  more  striking  proofs  of  the  output  of 
energy  in  their  muscular  movements,  for  example,  in  running, 
swimming,  and  flying.  Various  machines,  also,  enable  us  to 
make  use  of  different  forms  of  energy,  and,  as  we  shall  now 
see,  one  kind  of  energy  may  be  readily  transformed  into 
another  by  means  of  these  machines.  Suppose  we  consider 
the  work  that  goes  on  in  an  electric  power  plant.  The  coal 
that  is  shoveled  into  the  fire-box  beneath  the  boilers  by  the 
process  of  oxidation  liberates  heat,  which  is  one  of  the  forms 
of  energy.  The  heat  changes  the  water  into  steam,  which 
expands  and  so  exerts  its  power  to  run  the  engine,  and  thus 
heat  energy  is  transformed  into  the  energy  of  motion.  When 
the  engine  is  connected  with  a  dynamo,  this  energy  of  mo- 

1  If  a  difference  in  the  reading  of  the  two  thermometers  is  evident, 
this  difference  should  be  computed  in  the  later  readings  on  the  ther- 
mometers. 


66  PLANT  BIOLOGY 

tion  is  changed  into  electrical  energy,  and  this  in  turn  may  be 
converted  into  light  or  heat  energy  in  our  houses  or  into  energy 
of  motion,  as,  for  instance,  in  the  running  of  a  trolley  car. 

77.  Source  of   the  energy  developed  in  living  things.  — 
In  all  these  marvelous  transformations  of  energy  that  we  have 
just  enumerated  no  new  energy  is  created  and  none  is  de- 
stroyed.    Whence,   then,    comes   this   abundant   supply   of 
energy?     We  shall  find  the  probable  answer  to  this  question 
in  considering  again  the  processes  carried  on  in  the  leaves  of 
plants.     From  the  sun  comes  the  radiant  energy  that  is  abso- 
lutely essential  for  the  activity  of  the  chlorophyll  bodies,  by 
which  carbohydrates  are  formed.     In  the  formation  of  these 
compounds,  the  sun's  radiant  energy  is  used  and  apparently 
disappears.1     In  reality,  however,  it  has  only  been  stored  in 
the  chemical  compounds  formed  thereby,  since,-  as  we  have 
said  above,  energy  cannot  be  destroyed. 

78.  Oxidation  as  a  means  of  liberating  energy.  —  Let  us 
now  refer  once  more  to  the  processes  that  take  place  in  an 
electric  power  plant.     We  have  just  said  that  the  energy  de- 
rived from  the  rays  of  the  sun  is  stored  up  in  the  wood,  coal, 
and  other  fuel.     In  order  to  set  free  from  these  compounds 
the  energy  they  contain,  the  wood  or  coal  must  be  burned,  or 
in  other  words  combined  with  oxygen.     Every  one  knows  that 
when  we  wish  to  secure  a  large  amount  of  heat  from  our  fuel 
we  open  wide  the  drafts  in  order  to  secure  a  plentiful  supply 
of  oxygen.     We  demonstrated  in  our  studies  in  oxidation 
that  whenever  a  substance  is  burned,  heat  energy  is  liberated 

1  The  authors  are  indebted  to  Mr.  Paul  B.  Mann  of  the  Morris 
High  School  Department  of  Biology  for  the  following  demonstration 
of  the  effectiveness  of  the  radiant  energy  of  the  sun.  Place  a 
radiometer  (usually  found  in  the  physics  equipment  of  schools)  in 
direct  sunlight,  and  then  remove  it  from  the  sun's  rays.  Try  also 
the  effect  of  an  electric  light  by  bringing  the  radiometer  near  the 
light  bulb,  and  then  slowly  removing  it  to  a  distance. 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS          67 

and  usually  light  is  seen.  The  energy  set  free  by  the  oxida- 
tion of  fuel  may  be  transformed  at  one  time  into  light,  at 
another  time  into  motion,  or  again  into  heat. 

It  is  probably  true  that  the  liberation  of  energy  in  living 
plants  is  somehow  due  to  the  action  of  oxygen.  The  pro- 
cess, however,  is  doubtless  extremely  complicated,  and  just 
what  takes  place  no  one  knows.  Certainly  oxygen  in  some 
form  is  essential  for  the  life  of  every  plant  and  animal.  That 
this  is  true  of  plants,  the  following  experiment  will  show. 

79.  To  prove  that  seeds  need  air  in  order  to  grow.  — 
Laboratory  Study  No.  39.     Demonstration  or  Home  Work. 

Secure  two  wide-mouthed  bottles  and  place  in  the  bottom 
of  each  a  wet  sponge  or  some  wet  blotting  paper,  and  pour 
enough  water  in  each  bottle  just  to  cover  the  sponge  or  paper. 
Fill  both  bottles  with  pea  seeds  that  have  been  soaked  in 
water  for  twenty-four  hours.  Insert  a  tightly  fitting  cork 
into  the  mouth  of  one  of  the  bottles  to  exclude  the  air.  Leave 
the  other  bottle  open  to  the  air,  and  add  enough  water  from 
day  to  day  to  make  up  for  the  loss  by  evaporation.  Put 
both  bottles  in  a  warm  place. 

1.  Describe  this  experiment,  showing  in  what  respects  the 

conditions  are  the  same  for  both  groups  of  seeds. 

2.  In  what  one  respect  do  the  two  groups  of  seeds  differ  ? 

3.  At  the  end  of  several  days  examine  both  bottles  of  seeds, 

and  state  your  observation  concerning  the  amount  of 
growth  in  each  bottle. 

4.  State  clearly  your  conclusion  as  to  the  necessity  of  air  for 

growth  of  pea  seedlings. 

80.  Relation  of  oxygen  and  carbon  dioxid  to  oxidation.  — 
We  have  now  demonstrated  that  seedlings  will  not  grow 
without  air.     Biologists  have  proved  conclusively  that  oxygen 
is  the  element  in  the  air  that  is  essential  for  the  work  of  all 
plants,  and  that  without  it  they  die.     Hence,  we  may  con- 
clude, as  in  the  case  of  the  furnace,  that  the  necessary  energy 


68  PLANT  BIOLOGY 

of  a  plant  is  in  some  way  set  free  by  oxygen  acting  upon 
plant  compounds.  When  oxidation  of  compounds  containing 
carbon  takes  place,  we  find  that  carbon  dioxid  is  produced 
(11).  Now  if  processes  like  oxidation  are  carried  on  in  plants, 
we  should  expect  to  find  that  CC>2  is  formed.  The  following 
experiment  proves  clearly  that  such  is  the  case. 

81.  To   prove   that   carbon   dioxid   is   formed   during   the 
growth  of  young  seedlings.  —  Laboratory  Study  No.  40. 

In  the  bottom  of  two  large  jars  (fruit  jars  will  answer) 
place  some  wet  blotting  paper.  Fill  one  of  the  jars  half  full  of 
germinating  peas,  and  place  a  small  wide-mouthed  bottle 
full  of  lime  water  on  top  of  the  seeds.  Screw  the  top  of  the 
jar  on  tightly.  In  the  other  jar  place  a  bottle  of  lime  water 
and  cover  as  in  the  previous  jar.  At  the  end  of  twenty-four 
hours  or  more  examine  the  lime  water  in  both  jars. 

1.  Describe  the  preparation  of  the  experiment. 

2.  Compare  the  condition  of  the  lime  water  in  both  jars. 

What  has  caused  the  change  in  the  lime  water  in  both 
jars? 

3.  Air,  as  we  proved,  contains  a  little  carbon  dioxid.     Bearing 

this  fact  in  mind,  account  for  the  difference  in  the  ap- 
pearance of  the  lime  water  in  the  two  jars. 

4.  What  gas,  therefore,  do  you  find  to  be  given  off  during 

the  growth  of  young  seedlings  ?    ' 

II.   RESPIRATION 

82.  Respiration  in  plants.  —  It  should  be  clear  from  our 
study  thus  far  that  all  plants  require  oxygen,  and  that  this 
oxygen  brings  about  in  plants  a  process  resembling  oxidation 
at  least  in  the  releasing  of  heat  and  other  forms  of  energy 
and  in  the  producing  of  carbon  dioxid.     These  various  pro- 
cesses take  place  in  each  living  plant  cell.     Hence,  every 
cell  uses  oxygen  and  must  necessarily  form  carbon  dioxid. 
This  process  which  goes  on  in  every  living  cell  is  respiration. 


THE  PRODUCTION  OF  ENERGY  IN  PLANTS 


69 


In  green  plants  during  the  night,  when  carbon  dioxid  is  not 
being  used  for  starch  manufacture,  this  gas  is  given  off  to  the 
surrounding  air,  which  probably  is  not  true  to  any  great 
extent  during  the  daytime.  The  taking  in  of  oxygen  and  the 
giving  off  of  carbon  dioxid  by  plants  corresponds  to  breath- 
ing in  animals.  This  exchange  of  gases  is  carried  on 
through  the  thin  walls  of  roots,  through  the  lenticels  of 
stems,  and  through  the  stomata  of  leaves.  The  process  of 
breathing  must  not  be  confused  with  that  of  carbohydrate 
manufacture,  and  the  following  outline  will  show  the  funda- 
mental difference  between  the  two. 


CARBOHYDRATE  MANU- 
FACTURE 

RESPIRATION  (INCLUDING 
OXIDATION) 

Where  carried  on 

In  cells  containing 

In  all  living  cells 

chlorophyll 

When  carried  on 

In  sunlight 

Throughout    life    of 

cell 

Substances  taken  from 

C02 

0 

air 

. 

Substance    formed    in 

Carbohydrates 

C02 

plant 

Waste    substance    ex- 

0 

C02 

creted  to  air 

Advantage  to  plant 

Manufacture  of  food 

Release  of  energy 

CHAPTER   VII 

REPRODUCTION   IN   PLANTS 

I.    THE  STRUCTURE  AND  FUNCTIONS  OF  FLOWERS 

83.  Necessity  of  plant  reproduction.  —  Every  one  knows 
that  plants  like  peas,  beans,  and  corn  live  but  one  year. 
Shrubs  and  trees,  while  they  often  live  for  many  years,  finally 
die.     This  is  true  of  all  plants.     It  is  evident,  therefore,  that 
unless  there  were  some  means  of  producing  new  plants  to 
take  the  place  of  those  now  living,  all  forms  of  plant  life 
would  soon  cease  to  exist.     The  process  by  which  new  plants 
are  formed  is  known  as  reproduction.     In  the  higher  plants 
this  process  is  carried  on  by  flowers,  the  function  of  which  is 
to  produce  seeds  which  will  develop  into  new  plants.     We  are 
now  to  study  the  various  parts  of  flowers  and  to  consider  the 
work  of  each  part  in  this  process  of  reproduction. 

84.  Study  of    tulip  flower  (spring    study).  —  Laboratory 
Study  No.  41. 

Material:  While  the  trillium  is  a  more  satisfactory  flower  for 
beginning  the  study  of  the  process  of  reproduction,  the  danger 
that  the  wild  flowers  will  become  exterminated  seems  to  make  the 
study  of  the  tulip  advisable,  especially  in  large  city  high  schools. 
The  two  flowers,  however,  are  usually  in  season  at  the  same  time, 
and  if  possible  at  least  a  few  of  the-  trilliums  should  be  secured  for 
demonstration.  If  this  is  impossible,  the  distinction  between  calyx 
and  corolla  should  be  taught  from  the  apple  blossom  or  other  com- 
mon flower, 

70 


REPRODUCTION  IN  PLANTS  71 

A.  Floral  envelopes. — Most  flowers  have  parts  shaped  more 

or  less  ijike  leaves  which  have  either  green  or 
bright  colors.  These  parts  are  arranged  in  one 
or  more  circles  and  make  up  the  floral  envelopes. 

1.  How  many  parts  are  there  in  the  floral  envelopes  of  a 

tulip?  State  the  color  or  colors  of  these  parts 
in  the  flower  you  are  studying. 

2.  When  there  are  two  circles  to  the  floral  envelopes,  an 

outer  composed  of  green  parts  and  an  inner  made 
up  of  brightly  colored  parts  (as  in  the  trillium  or 
the  apple  blossom),  distinct  names  are  given  to 
the  various  parts.  The  outer  circle  is  called  the 
calyx  and  its  parts  are  known  as  sepals;  the 
inner  circle  is  called  the  corolla  and  each  of  its 
parts  is  called  a  petal. 

a.  State  the  number  and  color  of  the  sepals  in  the 

calyx  of  the  trillium. 

b.  How  many  petals  do  you  find  in  the  corolla? 

Describe  their  color. 

3.  Draw  a  side  view  of  a  tulip  before  it  has  fully  opened. 

Label  flower-stalk  and  floral  envelopes. 

B.  Essential  organs.  —  In  the  central  part  of  the  flower  are 

the  organs  without  which  the  work  of  the  flower 
cannot  be  performed.  For  this  reason  they  are 
called  the  essential  organs. 

1.  The  organs  arranged  in  a  circle  just  within  the  floral 

envelopes  are  known  as  stamens.  State  the 
situation  and  the  number  of  stamens  in  the  tulip. 
What  is  the  number  of  stamens  in  the  trillium  or 
apple  blossom  ? 

2.  Each  stamen  consists  of  a  stalk  called  the  filament 

and  an  enlarged  part  known  as  the  anther. 
Name  and  describe  each  of  the  parts  of  a  stamen. 

3.  Make  a  drawing  twice  its  natural  size  of  one  of  the 

stamens.     Label  filament,  anther. 

4.  Find  a  flower  the  stamens  of  which  have  a  powdery 

substance  known  as  pollen.  Which  part  of  the 
stamen  produces  the  pollen  ? 

5.  The  organ  at  the  center  of  the  flower  is  called  the 

pistil.     It  consists  of  three  divisions  at  the  top 


72  PLANT  BIOLOGY 

which  together  are  known  as  the  stigma,  and 
the  remainder  of  the  pist|  known  as  the  ovary. 
Describe  the  pistil  of  the  tulip  (and  of  the  tril- 
lium)  as  to  position,  shape,  and  color  of  its  parts. 

6.  Make  a  drawing  twice  its  natural  size  of  the  pistil. 

Label  stigma,  ovary. 

7.  Cut  thin  cross  sections  of  a  well-developed  ovary, 

lay  them  on  a  dark-colored  background,  and 
study  one  or  more  of  them  with  a  magnifier  to 
make  out  the  following  parts :  wall  of  the  ovary, 
small  objects  within  the  ovary  known  as  ovules. 
(These  ovules  develop  into  seeds.)  Describe 
what  you  have  done  and  tell  what  you  have  seen. 

8.  Make  a  drawing  at  least  an  inch  in  diameter  of  a  cross 

section  of  the  ovary,  labeling  ovary  wall  and 
ovules. 

9.  (Optional.)     Make  a  drawing  (corresponding  in  size  to  that 

called  for  in  6  above)  of  a  lengthwise  section  of  the 
ovary  to  show  wall  of  ovary,  ovules.  Label. 

85.  Study  of  the  gladiolus  flower  (autumn  study).  Lab- 
oratory Study  No.  42. 

Note  to  the  teacher.  —  Be  careful  to  remove  each  flower 
close  to  the  central  stalk,  so  that  the  ovary  may  not  be  in- 
jured. 

A.   Parts  of  the  flower. 

1.  Remove  the  two  leaves  at  the  base  of  the  flower,  since 

these  leaf -like  organs  do  not  belong  to  the  flower. 
The  outer  brightly  colored  parts  of  the  flower  are 
called  the  floral  envelopes.  These  colored  parts 
unite  to  form  a  greenish  tube  below. 

a.  Count  and  record  the  number  of  divisions  of  which 
the  floral  envelopes  are  composed. 

6.  State  whether  or  not  these  divisions  are  all  of  the 
same  size. 

2.  The  slender  stalks  with  purple  tips,  inside  the  floral 

envelopes,  are  called  stamens.  How  many  sta- 
mens do  you  find? 


REPRODUCTION  IN  PLANTS  73 

3.  The  single  white  stalk  with  three  divisions  at  the  top 

is  the  upper  part  of  the  pistil.     The  dark  green 
body  below  the  tubular  part  of  the  floral  en- 
velopes is  the  lower  part  of  the  pistil. 
Is  the  top  of  the  pistil  in  the  flower  you  are  studying 
lower  or  higher  than  the  stamens  ? 

4.  Make  a  drawing,  natural  size,  of  the  side  view  of  the 

flower,  and  label  the  following  parts :  the  divided 
portion  of  the  floral  envelopes,  the  tubular  por- 
tion of  the  floral  envelopes,  the  stamens,  the 
pistil. 

B.  Essential  organs.  —  The  stamens  and  pistils  are  called 
the  essential  organs  of  flowers  because  without 
them  the  work  of  the  flower  cannot  be  performed. 

1.  Carefully  slit  open  the  tubular  part  of  the  floral 

envelopes  down  to  the  lower  part  of  the  pistil. 
Then  remove  the  floral  envelopes,  leaving  the 
entire  pistil  uninjured. 

a.  State  what  you  have  done. 

b.  To  what  are  the  stamens  attached  ? 

c.  The  enlarged  part  at  the  top  of  the  stamen  is 

called  the  anther,  the  stalk-like  part  is  called  the 
filament.  Name  and  describe  the  parts  of  a 
stamen. 

2.  Make  a  drawing,  natural  size,  of  a  portion  of  the  floral 

envelope  to  which  a  stamen  is  attached.  Label 
division  of  floral  envelopes,  anther,  filament. 

3.  Find  a  flower  the  stamens  of  which  have  a  powdery 

substance  known  as  pollen.  Which  part  of  the 
stamen  produces  the  pollen  ? 

4.  The  pistil  consists  of  an  enlarged  portion  at  the  base 

called  the  ovary,  a  stalk-like  portion  called  the 
style,  and  a  spreading  portion  at  the  top,  each 
part  of  which  is  called  a  stigma.  Name  and 
describe  each  part  of  the  pistil. 

5.  Make  a  drawing,  natural  size,  of  the  pistil  and  label 

ovary,  style,  stigmas. 

6.  Cut  thin  cross  sections  of  a  well-developed  ovary,  lay 

them  on  a  dark-colored  background,  and  study 
one  or  more  of  them  with  a  magnifier  to  make 


74 


PLANT  BIOLOGY 


out  the  following  parts:  wall  of  ovary,  small 
objects  within  the  ovary  known  as  ovules. 
These  ovules  develop  into  seeds.  Describe  what 
you  have  done  and  tell  what  you  have  seen. 

7.  Make  a  drawing  at  least  an  inch  in  diameter  of  a 

cross  section  of  the  ovary,  labeling  ovary  wall, 
ovules. 

8.  (Optional.)     Make  a  drawing  (corresponding  in  size  to  that 

called  for  in  7  above)  of  a  lengthwise  section  of  the 
ovary  to  show  wall  of  ovary,  ovules.  Label. 

86.    Pollination.  —  We  have  learned  in  our  study  of  flowers 
that  pollen  is  produced  in  the  anther  of  the  stamen,  and  ovules 

in  the  ovary  of  the  pistil. 
Before  an  ovule  can  develop 
into  a  seed,  however,  certain 
portions  of  a  pollen  grain 
and  of  an  ovule  must  be 
combined.  Pollen  must, 


stigma 


•petal 


therefore, 
from    the 


be     transferred 
anthers    to    the 


FIG.  24.  — Structure  of  a  plum  blossom,    pistils,  and  to  this  process  is 

(Bailey.)  given  the  name  pol- 

lination. We  shall  now  learn  by  experiment  some 
adaptations  of  the  pistil  for  receiving  and  holding 
the  pollen. 

87.  Experiment  to  show  pollina- 
tion. —  Laboratory  Study  No.  43. 

Rub  a  small  brush  or  the  end  of 
a  toothpick  over  a  stamen  (e.g. 
tulip,  Easter  lily,  or  gladiolus)  which 
has  an  abundance  of  pollen,  and 

then  brush  this  pollen  Over  the  SUr-        escaping  from  the  anther  of 
face  of  the  Stigma.  a  stamen.  —  (Bailey.) 


REPRODUCTION  IN  PLANTS 


75 


1.  Describe  what  you  have  done. 

2.  Examine  the  surface  of  the  stigma  with  a  magnifier  and 

state  what  causes  the  pollen  to  stick  to  the  stigma. 

88.  Microscopical  Demonstration  of  Pollen  Grains  and  their 
Development.  —  Laboratory  Study  No.  44.  (Optional.)  Prepare 
some  sugar  solution  by  adding  to  ten  teaspoonfuls  of  water  one 
teaspoonful  of  molasses  or  grape  sugar  and  heat  to  boiling  point. 
Put  some  of  this  sugar  solution  in  a  clean  Syracuse  watch 
glass.  When  the  solution  has  cooled,  mix  with  it  some  pollen 
from  the  flower  of  a  tulip,  a  trillium,  a  sweet  pea,  or  nasturtium. 
Several  of  these  glasses  might  well  be  prepared  with  slightly  dif- 
ferent strengths  of  sugar  solution  and  piled  one  above  the  other  to 
keep  out  mold  spores.  Leave  the  glasses  until  the  pollen  grains 
have  germinated.  Study  the  preparation  with  the  low  power  of 
the  compound  microscope. 

1.  Find  some  pollen  grains  that  have  not  begun  to  grow  tubes. 
Describe  the  form  of  one  of  the  pollen  grains. 


FIG.  26.  —  Different  kinds  of  pollen  grains,  highly  magnified,  two  of  them 
forming  pollen  tubes.  —  (Duggar.) 


76 


PLANT  BIOLOGY 


2.  Find  several  grains  that  have  formed  tubes.     What  is  the 

color  and  shape  of  the  tubes  ? 

3.  Make  a  drawing  at  least  a  hah7  inch  in  diameter  of  a  pollen 

grain  before  it  has  sprouted  and  a  drawing  of  another  grain 
that  has  sprouted.     Label  pollen  grain,  pollen  tube. 

89.  Pollination,  germination  of  pollen  grains,  and  fertili- 
zation. —  We  have  now  learned  that  pollen  by  the  process  of 
pollination  is  carried  to  the  stigma  of  the  pistil  and  adheres 
to  the  stigma  by  a  sticky  substance  which  is  easily  seen  on 
the  stigma  of  the  Easter  lily  and  often  by  hairs,  also,  as  is  the 
case  in  the  tulip  and  gladiolus.  It  has  been  proved  that  this 
sticky  substance  contains  sugar  which  together  with  other 
materials  furnishes  food  for  the  growth  of  pollen  tubes  (see 
88).  As  each  tube  forms,  it  makes  its  way  down  through 
the  stigma  and  style  (if  present),  and  finally  reaches  an  ovule 
in  the  ovary.  The  tip  of  the  tube  now  penetrates  an  opening 
called  the  micropyle  (Greek,  micro  =  small  -\-pula  =  gateway) 

in  the  ovule.  Part  of 
the  living  substance  of 
the  pollen  grain  now 
unites  with  a  part  of 
the  living  substance  of 
the  ovule.  This  union 
is  known  as  fertilization. 
After  fertilization  has 
taken  place  the  ovule 
develops  into  a  seed. 

90.    The  cellular  na- 
ture of  pollen  and  ovules. 

—  (If  flowers  are  studied 
-  ^e  autumn,  it  is  sug- 

nified.  — (After  Strasburger.)  gested  that  this  Section 


\  sperm 
/nuclei 


tube 
nucleus 


REPRODUCTION  IN  PLANTS  77 

be  omitted  until  after  the  cellular  structure  of  plants  has  been 
considered.)  When  the  pollen  grains  are  first  formed  in  the 
anther,  each  consists  of  a  single  cell.  Later  the  nucleus  of 
this  cell  divides  and  forms  two  nuclei,  one  of  which  is  the 
generative  nucleus.  The  generative  nucleus  then  divides 
and  forms  two  sperm  nuclei.  The  ovule  is  more  complex 
in  its  structure,  being  composed  of  many  cells  of  different 
kinds.  But  here,  as  is  the  case  with  the  pollen  grain,  there  is 
one  important  cell  that  is  essential  in  the  process  of  reproduc- 
tion, and  this  is  known  as  the  egg-cell  (Figs.  27  and  29,  A). 

91.  The  formation  of  an  embryo.  —  When  the  pollen 
grain  germinates  and  forms  the  tube,  the  sperm  nucleus  is 
carried  by  the  tube  down  through  the  stigma  and  style  into 
the  cavity  of  the  ovary,  and  finally  through  the  micropyle  of 
the  ovule,  until  one  of  the  sperm  nuclei  comes  to  lie  beside 
the  nucleus  of  the  egg-cell.  The  two  nuclei  now  unite  in  the 
process  of  fertilization  to  form  a  fertilized  egg-cell.  The 
nucleus  of  this  cell  then  divides  and  later  the  cell-body,  thus 
forming  two  distinct  cells.  Each  of  these  divides  to  form  two 
cells,  and  the  four  cells  thus  produced  give  rise  to  eight,  then 
sixteen,  thirty-two,  and  so  on,  until  a  many-celled  structure 
is  developed  which  is  a  miniature  plant  called  the  embryo. 
This  embryo,  together  with  other  parts  of  the  ovule,  consti- 
tutes the  seed.  Some  of  the  cells  of  the  embryo  will  later 
form  the  roots,  others  the  stem,  and  still  others  the  leaves 
of  the  plant  (Fig.  29,  A-E). 

Hence,  the  new  plant  formed  by  this  method  of  reproduc- 
tion is  clearly  descended  from  two  different  parents,  one 
parent  flower  furnishing  in  its  pistil  the  egg-cell  and  the 
other  in  its  stamen  the  fertilizing  pollen.  We  may,  therefore, 
give  the  following  as  a  general  definition  of  the  process  we 
are  studying :  Fertilization  is  the  union  of  the  nucleus  of 


T8 


PLANT  BIOLOGY 


,X^WAMt  l/UX&Oo 
,'kJlt,  -WMC&U^ 

v-/3^ 


od&cl  staat  of  eWrtyxr 
0     l>  '       7 


FIG.  28.  —  Diagram  of  a 
longitudinal  section  of  a 
pistil  showing  germination 
of  pollen  grains. 

a   sperm  cell  with   the 
nucleus  of  an  egg-cell. 
Only  one  pollen  grain  or 
sperm  cell  can  be  used  in 
fertilizing     each     egg-cell, 
Usually,  however,  far  larger 
numbers  of  pollen  grains  be- 
come attached  to  the  stigma 
than  can   be  used   by  the 
ovules  in  the  ovary.    All  the 
pollen  grains  that  germinate 

produce  pollen  tubes  which  FlG.  29.  ^Fertilization  of  an  ovule  and 
may  be  Said  to  begin  a  the  early  stages  in  the  development  of 
race  down  the  Stigma  and  ^^mbryo.- (Diagrammatic.) 

style.  The  tubes  that  first  enter  ovules  are  the  ones  that 
carry  on  the  process  of  fertilization.  Those  that  are  beaten 
in  the  race  are  of  no  further  use  and  therefore  die. 


REPRODUCTION  IN  PLANTS  79 

92.  Self-pollination    and    cross-pollination.  —  Pollination, 
we  have  said,  is  the  transfer  of  pollen  from  the  anther  to  the 
stigma.     When  the  pollen  is  carried  from  the  anther  of  a 
flower  to  the  stigma  of  the  pistil  of  the  same  flower,  the  pro- 
cess is  known  as  self-pollination.     In  many  of  the  flowers 
that   are  self-pollinated,    the   anthers   are   above   the  stig- 
mas, and  when  the  pollen  is  ripe,  the  anthers  burst  open  and 
allow  the  pollen  grains  to  fall  upon  the  stigma  or  stigmas. 

If  pollen  is  carried  from  the  anther  of  a  flower  to  the  stigma 
of  the  pistil  of  a  flower  of  the  same  kind  but  on  another  plant, 
this  transfer  is  called  cross-pollination.  Cross-pollination  is. 
often  accomplished  by  the  help  of  the  wind,  as  in  the  flowers 
of  the  corn,  of  grasses,  and  of  many  trees.  In  these  cases  the 
pollen  is  dry  and  light,  and  the  pistils  are  usually  hairy  or 
feathery  to  catch  and  hold  the  pollen  grains. 

Most  bright-colored  and  sweet-scented  flowers  (like  the 
pansy  and  the  clover)  are  visited  by  bees  or  other  hairy  in- 
sects which  carry  pollen  on  their  mouth  parts,  bodies,  and 
legs  from  one  flower  to  another,  thus  insuring  cross-pollina- 
tion. We  shall  now  study  the  pansy  as  a  type  of  insect  polli- 
nated flowers. 

93.  Adaptations    of    the    pansy    for    cross    pollination.  - 
Laboratory  Study  No.  45. 

A.  Floral  envelopes.  —  When  there  are  two  circles  to  the  floral 
envelopes,  an  outer  composed  of  green  parts 
and  an  inner  made  up  of  brightly  colored  parts 
as  in  the  pansy,  distinct  names  are  given  to  the 
various  parts.  The  outer  circle  is  called  the 
calyx,  and  its  parts  are  known  as  sepals;  the 
inner  circle  is  called  the  corolla,  and  each  of  its 
parts  is  called  a  petal. 

1.  State  the  number  and  color  of  the  sepals. 

2.  How  many  petals  are  there?     Describe  the  color  or 

colors  of  each. 


80  PLANT  BIOLOGY 

3.  Locate  the  pairs  of  petals  that  are  nearly  alike  in  size 

and  shape. 
State  the  position  of  the  odd  petal. 

4.  On  which  of  these  petals  do  you  find  the  most  strik- 

ing spots  or  lines  of  color  ? 

5.  Make  a  drawing  of  the  pansy  in  its  natural  position, 

front  view,  and  natural  size.  Label  top  petals, 
side  petals,  lower  petal,  hairs  on  side  petals, 
color  spots. 

6.  Remove  the  two  upper  petals,   and  the  two  side 

petals.  Now  observe  the  tapering  projection 
on  the  lower  or  odd  petal  extending  upward  and 
backward  between  the  sepals.  This  is  called 
the  spur. 

a.   Tell  what  you  have  done  and  seen. 

6.  Carefully  remove  the  lower  petal  with  the  spur 
attached,  and  make  a  drawing  of  it,  natural 
size.  Label  the  spur  and  color  spot. 

7.  Slit  open  the  spur.     Is  the  spur  hollow  or  solid  ? 

8.  The  spur  contains  a  sweet  liquid  called  nectar  which 

attracts  the  bees  and  other  insects.  If  you  find 
any  nectar,  describe  it  and  tell  how  you  found 
it.  Describe  the  taste  of  the  nectar. 

9.  In  what  two  ways,  therefore,  may  pansies  attract 

bees? 

10.  On  which  petal  would  a  bee  be  most  likely  to  alight 

in  visiting  a  pansy?  What  is  there  on  this 
petal  to  guide  the  bee  toward  the  supply  of 
nectar  ? 

11.  (Optional.)   What  structures  on  the  side  petals  might  make 

it  difficult  for  the  bee  to  insert  its  mouth  parts  in 
this  region  ? 
B.  Stamens. 

1.  Observe  the    stamens    arranged    around  the  pistil. 

Carefully  separate  them  with  a  needle  or  pin. 
State  the  number  and  situation  of  the  stamens. 

2.  Carefully  bend  two  or  more  stamens  away  from  the 

pistil,  and  with  the  help  of  a  magnifier  look 


EEPRODUCTION  IN  PLANTS 


81 


on  their  inner  surface.  Tell  what  you  have 
done,  and  state  whether  the  openings  in  the 
yellow  anthers  from  which  the  pollen  is  dis- 
charged are  found  on  the  inner  surface  (next 
the  pistil)  or  on  the  outer  surface  of  the  anther. 

C.  Pistil. 

1.  Examine  the  pistil  after  the  stamens  have  been  re- 

moved. Carefully  describe  the  three  parts 
(ovary,  style,  and  stigma)  of  which  it  is  com- 
posed. 

2.  Observe  a  tiny  cavity  on  the  tip  of  the  stigma.     The 

inside  of  this  cavity  is  the  real  stigma  or  stig- 
matic  surface.  Describe  the  shape  and  state 
the  situation  of  the  stigmatic  surface. 

D.  Cross-pollination  of  the  pansy  by  bumblebees. 

1.  Hold  a  pansy  in  its  natural  position. 

a.  State  the  situation  of  the  stamens  with  reference 

to  the  odd  petal  (i.e.  are  they  above  or  below 
this  petal?). 

b.  On  what,  therefore,  will  pollen  probably  fall  if  it 

is  shaken  out  of  the  anthers  ? 

2.  To  determine  whether  or  not  what  you  have  just 

stated  is  true,  thrust  a  slender  tooth-pick  under 

the  stigma  and  then  under 

the  stamens  and  into  the 

spur.       Shake   the    flower 

gently  and  then  withdraw 

the  tooth-pick  and  examine 

the   surface  with   a   hand 

magnifier.     Tell  what  you 

have  done  and  state  whether 

or  not  pollen  is  found  on 

the  tooth-pick. 

3.  Examine  a  bumblebee.     On  what 

part  of  the  insect  (i.e. 
mouth-parts,  head,  or  body) 
would  the  pollen  be  most 
likely  to  fall  when  the  bee 


FIG.  30.  — Head  of  a 
bee. 


82 


PLANT  BIOLOGY 


FIG.  31.— Hind 
leg  of  a  worker 
bee. 


thrusts  its  mouth-parts  into  the 
spur  as  you  have  just  done  with 
the  tooth-pick?  How  are  all 
these  parts  adapted  to  hold 
pollen?  (Compare  with  Figs. 
30,  31.) 

4.  Still  holding  the  pansy  in  its  natural 

position,  notice  and  state  the  posi- 
tion of  the  stigma  with  reference 
to  the  odd  petal. 

5.  Now  push  a  tooth-pick  which  has  pollen 

on  it,  a  second  time  into  the  spur. 
State  whether  or  not  the  tooth- 
pick hits  the  stigmatic  cup  before 
you  get  it  under  the  stigma. 

6.  Why,  therefore,  will  a  bee  that  has  just 

been  to  one  pansy  flower  be  almost 
certain  to  deposit  pollen  on  the  stigmatic  cup 
of  the  next  pansy  it  visits  ? 


7.  (Optional  home  work.)  Write  a  paragraph  on  "The  Visit 
of  a  Bee  to  a  Pansy  Blossom,"  giving  a  complete 
account  of  what  the  bee  does  and  how  it  does  it. 

94.  The  advantages  of  cross-pollination  in  the  pansy.  —  Charles 
Darwin,  the  great  English  biologist,  proved  by  a  long  series  of  experi- 
ments that  seeds  produced  as  the  result  of  cross-pollination  develop 
into  far  more  healthy  plants  than  do  the  seeds  which  are  formed 
after  self-pollination.  Among  the  plants  with  which  he  experi- 
mented was  the  pansy  (Viola  tricolor).  He  planted  in  each  of  five 
pots  seeds  that  had  been  produced  by  cross-pollination,  and  an  equal 
number  of  seeds  that  were  the  result  of  self-pollination.  The  results 
of  the  experiments  are  given  in  his  own  words  as  follows:  "The 
average  height  of  the  fourteen  crossed  plants  is  here  5.58  inches, 
and  that  of  the  fourteen  self-fertilized  2.37 ;  or  as  100  to  42.  In 
four  of  the  five  pots,  a  crossed  plant  flowered  before  any  one  of  the 
self -fertilized ;  as  likewise  occurred  with  the  pair  raised  during  the 
previous  year.  These  plants  without  being  disturbed  were  now 


REPRODUCTION  IN  PLANTS  83 

turned  out  of  their  pots  and  planted  in  the  open  ground,  so  as  to 
form  five  separate  clumps.  Early  in  the  following  summer  (1869) 
they  flowered  profusely,  and'  being  visited  by  humble-bees  set 
many  capsules  which  were  carefully  collected  from  all  the  plants 
on  both  sides.  The  crossed  plants  produced  167  capsules,  and  the 
self-fertilized  only  17 ;  or  as  100  to  10.  So  that  the  crossed  plants 
were  more  than  twice  the  height  of  the  self-fertilized,  generally 
flowered  first,  and  produced  ten  times  as  many  naturally  fertilized 
capsules. 

"By  the  early  part  of  the  summer  of  1870  the  crossed  plants  in 
all  the  five  clumps  had  grown  and  spread  so  much  more  than  the 
self-fertilized,  that  any  comparison  between  them  was  superfluous. 
The  crossed  plants  were  covered  with  a  sheet  of  bloom,  whilst  only 
a  single  self-fertilized  plant,  which  was  much  finer  than  any  of  its 
brethren,  flowered.  The  crossed  and  self-fertilized  plants  had  now 
grown  all  matted  together  on  the  respective  sides  of  the  superficial 
partitions  still  separating  them ;  and  in  the  clump  which  included 
the  finest  self-fertilized  plant,  I  estimated  that  the  surface  covered 
by  the  crossed  plants  was  about  nine  times  as  large  as  that  covered 
by  the  self-fertilized  plants.  .  .  . 

"The  ensuing  winter  was  very  severe,  and  in  the  following  spring 
(1871)  the  plants  were  again  examined.  All  the  self-fertilized 
were  now  dead,  with  the  exception  of  a  single  branch  on  one  plant, 
which  bore  on  its  summit  a  minute  rosette  of  leaves  about  as  large 
as  a  pea.  On  the  other  hand,  all  the  crossed  plants  without  excep- 
tion were  growing  vigorously.  So  that  the  self -fertilized  plants, 
besides  their  inferiority  in  other  respects,  were  more  tender. 

"Another  experiment  was  now  tried  for  the  sake  of  ascertaining 
how  far  the  superiority  of  the  crossed  plants,  or  to  speak  more  cor- 
rectly, the  inferiority  of  the  self-fertilized  plants,  would  be  trans- 
mitted to  their  offspring.  The  one  crossed  and  one  self-fertilized 
plant,  which  were  first  raised,  had  been  turned  out  of  their  pot  and 
planted  in  the  open  ground.  Both  produced  an  abundance  of  very 
fine  capsules,  from  which  fact  we  may  safely  conclude  that  they  had 
been  cross-fertilized  by  insects.  Seeds  from  both,  after  germinating 
on  sand,  were  planted  in  pairs  on  the  opposite  sides  of  three  pots. 


84  PLANT  BIOLOGY 

The  naturally  crossed  seedlings  derived  from  the  crossed  plants 
flowered  in  all  three  pots  before  the  naturally  crossed  seedlings 
derived  from  the  self -fertilized  plants. 

"The  average  height  of  the  six  tallest  plants  derived  from  the 
crossed  plants  is  12.56  inches;  and  that  of  the  six  tallest  plants 
derived  from  the  self-fertilized  plants  is  10.31  inches ;  or  as  100  to 
82.  We  here  see  a  considerable  difference  in  height  between  the 
two  sets,  though  very  far  from  equalling  that  in  the  previous  trials 
between  the  offspring  from  crossed  and  self-fertilized  flowers.  This 
difference  must  be  attributed  to  the  latter  set  of  plants  having  in- 
herited a  weak  constitution  from  their  parents,  the  offspring  of  self- 
fertilized  flowers ;  notwithstanding  that  the  parents  themselves  had 
been  freely  intercrossed  with  other  plants  by  the  aid  of  insects." 
("  Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom.") 

Darwin,  therefore,  proved  conclusively  by  these  careful 
experiments  (1)  that  pansy  blossoms  which  were  cross-polli- 
nated produced  ten  times  as  many  seeds  as  those  that  were 
self -pollinated ;  (2)  that  the  plants  developed  from  these 
seeds,  produced  as  a  result  of  cross-pollination,  were  far  more 
vigorous  and  prolific ;  and  (3)  that  the  descendants  of  the 
plants  produced  by  self-pollination,  even  when  their  flowers 
were  cross-pollinated,  were  not  able  to  develop  seeds  capable 
of  as  vigorous  growth  as  the  descendants  of  plants  produced 
continuously  by  cross-pollination. 

95.  Prevention  of  self-pollination.  —  We  have  found  that 
the  pansy  is  well  adapted  to  bring  about  cross-pollination, 
and  since,  as  Darwin  proved,  cross-pollination  results  in  seeds 
being  formed  which  produce  much  more  vigorous  and  fruit- 
ful plants,  we  should  expect  that  the  pansy  would  have  de- 
veloped some  means  of  preventing  self-pollination ;  and  this, 
as  we  shall  see,  proves  to  be  the  case. 

The  anthers  of  the  pansy,  as  we  saw,  are  joined  about  the 
pistil  so  as  to  form  a  band,  and  the  openings  for  the  escape  of 


REPRODUCTION  IN  PLANTS  85 

pollen  are  on  their  inner  surfaces,  next  to  the  style  and  ovary. 
When  the  pollen  is  shaken  out  of  the  anthers,  it  first  collects 
in  the  space  between  the  anthers  and  the  pistil.  In  the  natu- 
ral position  of  the  pansy  blossom  it  should  be  remembered 
that  the  pistil  is  directed  downward,  and  the  end  of  the  stigma 
rests  on  the  lower  petal,  with  the  stigmatic  cup  opening  out- 
ward and  away  from  the  anthers.  Between  the  two  anthers, 
on  the  under  side  of  the  pistil,  and  at  the  end  nearest  the 
stigma,  there  is  a  V-shaped  notch  from  which  the  pollen  may 
readily  escape  when  the  flower  is  shaken  by  the  wind  or 
insects.  Since  the  notch  is  immediately  over  the  groove  in  the 
lower  petal,  the  pollen  falls  into  this  groove  and  cannot  un- 
aided get  into  the  stigmatic  cup,  since,  as  before  stated,  this 
cup  opens  away  from  the  direction  in  which  the  pollen  must 
fall.  That  the  pansy  pretty  effectually  prevents  self-polli- 
nation the  following  results  of  some  of  Darwin's  experiments 
along  this  line  show.  Two  vigorous  pansy  plants  were 
selected  for  the  experiment.  One  was  covered  with  a  net  so 
that  the  bumblebees  could  not  get  at  the  flowers,  and  the 
other  was  left  uncovered.  In  the  uncovered  one  105  fine 
capsules  were  formed,  while  on  the  covered  one  only  18  were 
formed,  and  in  these  only  a  few  good  seeds  developed; 
and  Darwin  states  that  even  the  few  seeds  formed  were  prob- 
ably due  to  the  agency  of  tiny  insects  that  the  net  could  not 
exclude. 

In  many  other  flowers  in  which  both  pistil  and  stamens  are 
present  we  find  other  devices  for  preventing  self-pollination. 
Some  of  these  are  as  follows:  In  apple  and  pear  blossoms 
the  stamens  usually  ripen  at  different  times  from  the  stigmas 
in  the  same  blossom,  so  that  self-pollination  in  such  cases  is 
impossible.  Likewise,  when  stamens  and  pistils  are  in  differ- 
ent flowers,  as  in  the  pumpkin,  corn,  and  willow,  cross-polli- 
nation is  obviously  necessary,  if  seeds  are  to  be  formed. 


86 


PLANT  BIOLOGY 


Moreover,  in  case  cross-  and  self-pollination  take  place  in  a 
given  flower,  it  has  been  proved  that  the  pollen  from  another 
flower  will  usually  grow  down  the  pistil  more  rapidly  than  the 
pollen  produced  in  the  same  flower,  and  so  in  such  cases  fer- 
tilization is  more  likely  to  result  from  cross-pollination  than 
from  self-pollination. 

96.  Cross-pollination  by  insects.  —  From  our  study  of  the 
pansy  we  learned  that  insects  are  attracted  by  bright  colors 
and  sweet  odors.  By  many  observations  biologists  have 


FIG.  32.  —  A,  staminate  squash  blossom  ;  B,  pistillate  squash  blossom. 
(Bailey.) 

learned  that  most. flowers  with  these  characteristics  are  vis- 
ited by  insects,  and  that  these  animals  carry  pollen  from 
blossom  to  blossom,  thus  insuring  cross-pollination.  Any 
one  familiar  with  apple,  pear,  or  other  fruit  trees  has  seen 
that  at  time  of  blossoming  these  trees  are  alive  with  buzzing 
bees,  and  fruit  growers  know  that  were  it  not  for  these  insect 
visitors  their  fruit  crops  would  prove  a  failure.  Some 
plants  (the  squash,  for  example)  have  two  kinds  of  flowers, 
one  kind  containing  stamens,  the  other  pistils.  It  is  evident, 
therefore,  from  what  we  have  already  learned  that  pollina- 


REPRODUCTION  IN  PLANTS 


87 


tion,  fertilization,  and  the  development  of  fruit  and  seeds 
could  not  take  place  in  plants  like  these  if  there  were  not 
some  means  of  transferring  pollen  from  the  staminate 
flowers  to  pistillate  flowers.  One  has  only  to  watch  squash 

blossoms  on  a  sunny  day 
to  know  that  bees  visit 
them  in  great  numbers  and 
that  their  hairy  bodies  are 
dusted  with  yellow  pollen 
as  they  fly  from  flower  to 
flower. 


FIG.  33.  —  Corn  stalk  with  "  tassels  "  (stam- 
inate flowers)  at  the  top. —  (Duggar.) 


FIG.  34.  —  Developing  ear 
of  corn  (pistillate  flowers). 
—  (Bailey.) 


97.  Cross-pollination  by  wind.  —  There  are  many  plants, 
however,  which  have  flowers  without  conspicuous  color  or 
odor;  among  these  are  the  grasses,  the  corn,  and  many 
common  trees  like  the  oaks,  birches,  and  pines.  At  the  top 
of  the  corn  stalk  in  midsummer  develop  the  "  tassels," 
and  when  these  are  shaken,  they  scatter  great  quantities  of 


88  PLANT  BIOLOGY 

light,  dry  pollen.  On  another  part  of  the  plant  the  ears  of 
corn  develop.  Each  ear  consists  in  part  of  clusters  of  pistillate 
flowers,  and  the  threads  of  silk  represent  the  styles  of  the 
pistils.  Farmers  know  that  a  single  corn  plant,  growing  in  a 
place  apart  from  other  corn  plants,  will  not  form  vigorous 
ears.  To  secure  a  good  crop,  pollen  must  be  carried  from  the 
tassels  of  one  plant  to  the  silk  of  another,  and  this  is  accom- 
plished in  a  garden  or  a  corn  field  by  the  wind.  Much  more 
pollen  must  be  produced,  however,  by  wind-  than  by  insect- 
pollinated  flowers,  since  in  the  former  case  a  great  deal  more 
is  wasted.  Many  wind-pollinated  flowers,  such  as  grasses, 
have  feathery  styles  to  catch  and  hold  the  pollen  brought  by 
the  wind. 

98.    Summary  and  definitions. 

Floral  envelopes  of  a  flower  =  calyx  +  corolla. 

Calyx:    composed    of    sepals    (often   green   in   color); 

principal  use,  to  inclose  and  help  protect  the 

essential    organs    from    cold,    rain,    or    biting 

insects. 
Corolla:   composed  of  petals  (usually  bright  colored); 

principal  use  to  attract  insects  and  so  secure 

cross-pollination. 

Essential  organs  of  a  flower  =  stamens  +  pistils. 

Stamens:  usually  composed  of  filament  and  anther; 
use,  to  produce  pollen  grains,  each  containing 
a  sperm-cell. 

Pistil:  usually  composed  of  ovary,  style,  and  stigma 
(or  stigmas) ;  use,  to  produce  ovules,  each  con- 
taining an  egg-cell,  and  to  insure  pollination, 
germination  of  pollen  grains,  and  fertilization. 


REPRODUCTION  IN  PLANTS  89 

II.   THE  STRUCTURE  AND  FUNCTIONS  OF  FRUITS 

99.  Relation  of  fruits  to  reproduction.  —  We  have  already 
learned  that  the  use  or  function  of  flowers  is  to  insure  the 
production  of  seeds.     As  is  generally  known,  seeds  are  found 
in  fruits.     We  are  now  to  study  several  types  of  fruits. 

100.  Study  of  the  bean  or  pea  fruit.  —  Laboratory  Study 
No.  46. 

A.  Outside  of  the  fruit. 

Study  if  possible  young  pods,  well-developed  pods,  and 
pods  that  have  dried;  or  charts  may  be  used 
to  show  the  developing  pods. 

1.  Name  and  describe  the  structure  which  attached  the 

pod  to  the  plant. 

2.  The  main  part  of  the  fruit  or  pod  is  the  pistil,  which 

in  the  bean  or  pea  flowers  consisted  of  ovary, 
style,  and  stigma.  Which  of  these  parts  are 
found  in  the  fruit  you  are  studying?  (Fig.  35.) 

3.  Bean  and  pea  blossoms  have  calyx,  corolla,  stamens, 

and  pistil.  What  parts  of  the  flower  are  present 
in  the  fruit?  What  parts  have  disappeared? 

4.  Make  a  drawing,  natural  size,  of  the  fruit  you  are 

studying  in  the  position  in  which  it  hung  on  the 
plant.  Label  fruit-stalk,  calyx  (if  present),  and 
the  parts  of  the  pistil  that  you  find. 

B.  Inside  of  the  fruit. 

Split  the  pod  lengthwise  into  halves. 

1.  Carefully  move  one  of  the  seeds  in  the  pod  ;  is  it  free 

from  the  pod,  or  is  it  attached  ? 

2.  (Optional.)     The  region  of  an  ovary  to  which  seeds  are 

attached  is  called  the  placenta  (as  was  also  the  case 
in  the  ovary  of  flowers).  Locate  the  placenta  in  the 
fruit  you  are  studying. 

3.  (Optional.)     State  whether  or  not  you  find  any  undeveloped 

seeds.  Undeveloped  seeds  probably  never  were  fer- 
tilized. 


90  PLANT  BIOLOGY 

4.  Draw,  natural,  size  in  the  position  in  which  the  pod 
hung  on  the  plant  the  opened  fruit.  Label  wall 
of  ovary,  developing  seeds  (undeveloped  seeds, 
if  present),  seed -stalk. 


^,     CITVtUAUl-   QVOUf 

FIG.  35.  —  Development  of  the  pea  fruit  from  the  pea  flower.  —  (Drawn 
from  Jung  Chart.) 

101.    Study  of  the  cucumber,  Tokay  grape,  cranberry,  or 
tomato  fruit.  —  Laboratory  Study  No.  47. 

A.  Outside  of  the  fruit. 

1.  All  of  the  fruits  named  above  are  developed  ovaries. 

Describe  the  shape  and  color  of  the  fruit  you  are 
studying. 

2.  Make  a  drawing,  natural  size  (or  an  inch  in  diameter 

in  case  the  grape  or  cranberry  is  used).     Label 
fruit-stalk  (if  present),  ovary. 

B.  Inside  of  the  fruit. 

Cut  a  cross  section  of  one  of  the  fruits  you  are  studying. 
1.    Carefully  move  one  of  the  seeds  within  the  fruit ;    is 
it  attached  or  is  it  free  ? 


REPRODUCTION  IN  PLANTS  91 

2.  Make  a  drawing,  natural  size  (or  an  inch  in  diameter 

in  case  the  grape  or  cranberry  is  used),  of  one 
half  of  the  fruit,  and  show  method  of  seed 
attachment. 

3.  (Optional.)     Pinch  a  seed  of  one  of  the  fruits  between  your 

thumb  and  forefinger.  Is  it  hard  or  soft  ?  Is  it  dry  or 
slippery?  Of  what  advantage  are  these  character- 
istics? 

102.  Seed  Dispersal.  —  It  is  evident  that  stronger  plants 
will  be  developed  from  seeds  if  the  latter  are  carried  some 
distance  from  the  mother  plant,  for  then  they  will  not  be 
shaded  by  the  mother  plant,  and  the  young  plants  will  have 
more  light,  air,  food,  and  moisture,  if  they  are  not  crowded 
together.     We  shall  now  study  some  of  the  devices  by  which 
plants  secure  the  dispersal  of  their  seeds. 

103.  Seed  dispersal  by  wind.  —  Laboratory  Study  No.  48. 
Study  one  or  more  of  the  following  fruits :  — 

A.    Winged  fruits. 

1.  The  maple  fruit. 

a.  Find  the  fruit  stalk,  the  two  cells  of  the  ovary  each 

containing  a  single  seed,  the  wing  attached  to 
each  cell  of  the  ovary. 

Hold  between  yourself  and  the  light  a  maple  fruit 
in  the  position  in  which  it  hung  on  the  tree,  and 
draw  it  (X  2).  Label  fruit-stalk,  cell  of  ovary, 
containing  one  seed,  wing,  veins  of  wing. 

b.  Hold  one  of  the  fruits  some  distance  above  the  desk 

and  let  it  fall.  Describe  the  movements  of  the 
fruit  in  falling. 

c.  Of  what  use  are  the  wings  if  the  wind  were  blowing 

while  the  fruit  is  falling,  or  after  the  fruit  has 
fallen  to  the  ground  ? 

d.  Is  the  maple  fruit  a  dry  or  a  fleshy  fruit  ? 

2.  The  linden  fruit. 

a.   Notice  the  wing-like  attachment  on  the  fruit-stalk. 
Do  the  linden  fruits  occur  singly  or  in  clusters? 


92 


PLANT  BIOLOGY 


Is  the  fruit  hard  or  soft  ?     Draw  in  the  position 
on  which  it  hung  on  the  tree  ( X  2)  the  fruit  that 
is    given   you.     Label    main  fruit-stalk,  wing- 
like  attachment,  single  fruit  stalk,  fruit. 
b.  c.  d.      Answer  questions  given  under  1  (above). 
3.   The  elm  fruit  or  ailanthus  fruit. 

a.  Notice  the  fruit  stalk,  the  single-celled  ovary,  the 

wing  about  the  ovary. 

Draw  ( X  2)  one  of  the  above-named  fruits.     Label 
fruit-stalk,  ovary,  wing. 

b.  c.  d.      Answer  questions  given  under  1  above. 

B.    Tufted  fruits  (or  seeds). 

1.  The  clematis,  dandelion,  thistle,  or  aster  fruit. 

a.  Find  the  tiny  seed-like  ovary,  containing  a  single 

seed,  and  the  tuft  of  hair.     Draw  ( X  2)  one  of 
the  fruits.     Label  ovary,  tufts  of  hair. 

b.  c.  d.     Answer  questions  under  A,  above. 

2.  The  milkweed  fruit  and  seed. 

a.  (Optional.)     Study  Fig.  36.     Describe  the  way  the  pod 

opens  when  it  is  ripe.     Are  the  seeds  many  or  few  ? 
Draw  one  of  the  fruits  (pods)  to  show  the  method  of 

opening.  Label  fruit-stalk, 
ovary,  seeds,  style. 

b.  Examine  one  of  the  seeds 

that  has  been  detached 
from  the  pod.  Draw 
(X2)  one  of  the  seeds 
with  its  tuft  of  hair. 
Label  seed,  tuft  of  hair. 

c.  Drop   one   of    the    tufted 

seeds  out  of  an  open  win- 
dow  when  a  breeze  is 
blowing  or  fan  a  seed 
in  the  laboratory.  State 
your  observation.  What 

FIG.    36.  —  Milkweed    pod  IS  One  US6   of   the  tuft  of 

opening.  hair  ? 


REPRODUCTION  IN  PLANTS  93 

104.    Seed  dispersal  by  animals.  —  Laboratory  Study  No. 
49.     Study  one  or  more  of  the  following  fruits: 

A.  Burs  and  stickers. 

1.  Cocklebur. 

a.  Hold  one  of  the  fruits  between  yourself  and  the 
light.  Do  the  hooks  all  curve  toward  one  end 
of  the  fruit  or  in  several  directions  ? 
Notice  the  two  larger  projections  at  one  end  of  the 
fruit.  These  are  the  styles.  Draw  (  X  2)  the 
outside  of  one  of  the  cockleburs,  showing 
the  direction  of  the  hooks.  Label  ovary, 
hooks,  two  styles  (large  prongs  at  one  end  of 
fruit). 

6.  Rub  one  of  the  cockleburs  on  a  rough  surface  of 
your  clothing  and  try  to  remove  it.  By  what 
means  does  it  cling  to  the  cloth?  How  is  a 
cow  or  other  hairy  animal  Adapted  to  disperse 
this  fruit? 

2.  Burdock. 

a.  Each  burdock  consists  of  a  large  number  of  indi- 

vidual fruits.  Hold  the  burdock  to  the  light. 
In  what  directions  do  the  hooks  extend  ?  Why 
is  this  an  advantage  in  securing  the  distribu- 
tion of  fruits? 

b.  Answer  questions  under  1  b  above. 

3.  Bidens  (also  called  pitchforks  or  beggar's  ticks). 

a.  Hold  the  fruit  to  the  light  or  examine  it  with  a 

hand   magnifier.     In   what    direction    do   the 
little  barbs  on  the  two  prongs  of  the  ovary 
extend?     Why  is  this  an  advantage? 
Draw   (  X  2)   one  of    the  bidens  fruits.      Label 
ovary,  prongs,  barbs. 

b.  Answer  questions  in  1  b  above. 

B.  Fleshy  fruits.     Suggested  as  home  work. 

1.  In  what  ways  are  the  seeds  of  apples,  cherries,  and 
of  many  other  fleshy  fruits  protected  while  they 
are  ripening? 


94 


PLANT  BIOLOGY 


2.  Many  fleshy  fruits  are  dispersed  by  birds  and  other 

animals  which  are  seeking  food.     How  are  these 
animals  rewarded  for  doing  this  work? 

3.  How  are  the  seeds  of  ripe  peaches  and  cherries,  for 

example,  protected  from  injury? 

105.  Fruits  and  their  classification.  —  If  one  were  asked 
to  give  examples  of  fruits,  one  would  doubtless  give  such 
forms  as  apples,  cherries,  and  peaches.  But  it  is  doubtful 
if  he  would  think  of  including  among  fruits,  pea  pods,  pump- 
kins, chestnuts,  and  corn.  To 
the  botanist,  however,  these  are 


FIG.  37.  —  Lengthwise  sec- 
tion of  apple  fruit,  showing 
seeds  attached  to  a  central 
placenta.  —  (Bailey.) 


FIG.  38.  —  Cross  section  of  apple 
fruit,  showing  seeds  and  their  cov- 
erings which  constitute  the  core. 


considered  to  be  just  as  truly  fruits  as  the  forms  commonly 
thought  of  as  fruits.  Let  us  see  why  such  diverse  plant 
products  as  those  just  named  are  all  included  under  the  head- 
ing of  fruits.  Technically,  a  fruit  is  a  ripened  ovary  and  its 
contents  with  any  other  part  of  the  plant  that  is  closely  incorpo- 
rated with  it;  and  since  the  forms  named  above  are  all  ripened 
ovaries  containing  one  or  more  seeds,  it  is  evident  that, 
strictly  speaking,  they  must  be  classed  with  the  fruits  as 
much  as  apples  and  cherries. 

Sometimes  the  flower  contains  a  number  of  pistils  which 
form  a  pulpy  mass,,  such  as  the  raspberries  and  blackberries 


REPRODUCTION  IN  PLANTS 


95 


(see  Fig.  40) ;  hence  each  of  these  so-called  berries  is  composed 
of  a  number  of  separate  fruits.     Sometimes  the  end  of  the 
stem  which  bears  the  pistils  becomes  pulpy  and  juicy  and  the 
dry  pistils  are  embedded  in 
its  outer  surface,  as  is  the 
case  with  strawberries  (see 
Fig.   42).     In   other   fruits 
the  ovary  may  form  a  hard 
woody  wall,  as  in  the  nuts 
like  the  chestnut  (Fig.  39) 
and  acorn,  or  the  wall  may 
be  like  a  tough  paper,  as  in 
the  pods  of  peas  and  locusts 
(Fig.   43).      In   still    other 
forms  the  whole  ovary  may 
become  fleshy,  as  in  the  true 
berries,  such   as   the   cran- 
berry, grape,   and   tomato. 
Or  we  may  find  a  combina- 
tion of  a  tough  wall  and  a  fleshy  interior,  as  in  the  pumpkin, 
squash,  and  cucumber.     In  cherries,  plums,  and  peaches  the 
ovary  forms  two  kinds  of  material,  the  inner  very  hard  and 

stone-like  and  the  outer  pulpy. 
In  fruits  like  the  corn  grain 
and  the  wheat  kernel  the  ovary 
wall  is  so  closely  united  with 
the  coats  of  the  single  seed  that 
these  grains  are  commonly  con- 
sidered as  seeds. 

FIG.  40. —Raspberry  fruits.  ...  ,        ... 

The   facts   just  stated  with 

regard  to  different  kinds  of  fruits  suggest  a  simple  form  of 
classification,  based  largely  on  the  characteristics  of  the  ovary 
walls.  Thus,  for  instance,  all  those  fruits,  such  as  bean  pods, 


FIG.  39.  —  Chestnut   fruits  inside  the 
chestnut  bur.  —  (Bailey.) 


96 


PLANT  BIOLOGY 


grains,  and  nuts,  in  which  the  walls  are 
dry  at  maturity,  are  called  dry  fruits. 
Those  in  which  the  walls  are  pulpy 
throughout,  as  in  the  tomato,  are  termed 
fleshy  fruits;  and  those 
which  are  partly  fleshy 
andpartly  stone-like,  as 
F'G-  4J;  -  Flow,eRr  °f  thf  in  the  cherry  and  peach, 

strawberry.  —  (Bailey.)  *     . 

are  called  stone  fruits. 
Another  scheme  for  classifying  fruits  is 

based  upon  the  fact  that  some  fruits  break 

open  when  ripe  and  scatter  their  seeds, 
while  others  remain 
closed.  Examples  of 
fruits  of  the  first  kind 
are  the  bean,  milkweed,  and  pansy,  and 
of  those  that  remain  closed  are  cherries, 
apples,  and  grains.  Whether  or  not  a  fruit 
breaks  open  at  maturity  depends  upon 
the  character  of  the  ovary  wall,  and  this 
in  turn  determines,  as  we  shall  now  see, 
the  method  by  which  its  seeds  are  dis- 
persed. 


FIG.   42.  —  Straw- 
berry. —  (Bailey.) 


FIG.    43.  —  Pea   pod. 
(Bailey.) 


106.   Home   work   on   fruits.  —  Laboratory 
Study  No.  50.     (Optional.) 
Classify  the  fruits  with  which  you  are  familiar  in  a  table  like 
the  following : 


NAME 
OF  FRUIT 

DRY 

FRUIT 

FLESHY 

FRUIT 

STONE 
FRUIT 

OPEN 

WHEN 

RIPE 

CLOSED 

WHEN 

RIPE 

SEEDS 
DIS- 
PERSED 
BY  WIND 

SEEDS 
DIS- 
PERSED BY 
ANIMALS 

Cherry 

X 

X 

X 

CHAPTER  VIII 
PLANT   PROPAGATION 

I.    SEEDS  AND  THEIR  DEVELOPMENT  INTO  PLANTS 

107.  Study  of  the  bean  seed  and  the  development  of  the 
bean  seedling.  —  Laboratory  Study  No.  51. 

Materials:  Dry  bean  seeds  and  seeds  that  have  been  soaked  for 
24  hours.  Sprouted  bean  seeds  and  seedlings  grown  as  follows: 
To  secure  early  stages,  put  seeds  that  have  been  soaking  for  24  hours 
between  layers  of  wet  blotting  paper,  or  bury  them  in  moist  sawdust, 
and  allow  them  to  stand  in  a  warm  place  for  two  or  three  days. 
For  older  stages  of  bean  seedlings  plant  soaked  seeds  in  boxes  con- 
taining moist  sawdust,  sand,  or  earth.  If  some  of  these  boxes  are 
put  in  a  warm  place  and  others  in  a  cool  place  all  stages  may  be 
obtained  in  two  to  four  weeks. 

1.  What  difference  do  you  notice  in  the  size  of  the  dry  and 

soaked  seed?  How  do  you  account  for  this  dif- 
ference ? 

(Optional.)  Half  fill  a  bottle  with  dry  bean  seeds,  and  add 
water  enough  to  fill  the  bottle.  Allow  the  seeds  to 
soak  for  24  hours.  How  much  do  beans  increase  in  size 
when  soaked  ? 

2.  On  one  edge  of  a  soaked  seed  find  a  scar  called  the  hilwn, 

which  marks  the  place  where  the  bean  was  attached 
to  a  small  stem  which  connected  it  to  the  pod. 
Locate  the  hilum,  and  state  what  caused  this  scar. 

3.  Make  a  sketch  about  two  inches  long  of  the  seed,  show- 

ing the  edge  on  which  the  scar  is  found.     Label 
scar  or  hilum. 
H  97 


98 


PLANT  BIOLOGY 


4.  Pinch  a  soaked  seed,  and  notice  the  opening  near  the 

hilum  through  which  water  is  forced  from  the 
seed.  This  opening  is  called  the  micropyle  (Greek, 
micro  =  tiny  +  pula  =  gateway). 

a.  Describe  the  position  and  appearance  of  the  micro- 

pyle.    What  is  the  derivation  of  the  word  ? 

b.  Sketch  the  micropyle  in  your  drawing  in  3  above. 

5.  Carefully  remove    the    seed-coat   from  a  soaked  bean. 

All  the  structures  within  this  seed-coat  together 
.  form  a  little  bean  plant,  called  a  bean  embryo. 
Break  off  one  of  the  two  halves  and  make  out  the 
following  parts  of  thfe  bean  embryo:  1)  the  two 
thickened  halves  of  the  bean  called  the  seed  leaves 
or  cotyledons;  2)  a  little  sprout,  the  first  stem  or 
hypocotyl  (Greek,  hypo  =  beneath  +  cotyl  =  cotyle- 
don) ;  and  3)  the  two  tiny  folded  leaves  forming 
the  first  bud  or  plumule,  lying  between  the  cotyle- 
dons. 

a.  State  what  you  have  done  to  show  the  parts  of  the 

embryo. 

b.  Name  and  describe  each  of  these  parts. 

c.  Place  the  cotyledon  you  have  removed  close  to  its 

point  of  attachment  to 
the  hypocotyl,  and 
make  a  drawing  about 
two  inches  long,  show- 
ing all  the  parts  named 
above,  labeling  each 
part. 

6.  Examine  a  bean  seed  that 
has  just  begun  to 
sprout. 

a.  Name    the    part    of    the 

bean  embryo  that  first 
breaks  through  the 
seed-coats. 

b.  Make    a    drawing    about 

two   inches   long,    to 

FIG.  44.  —  Germination  of  castor  show      the      Sprouted 

bean.  —  (Osterhout.)  Seed.       Label. 


PLANT  PROPAGATION 


99 


7.  Look  at  a  pot  of  young  seedlings  that  are  just  pushing 

their  way  above  the  surface  of  the  soil  or  sawdust, 
a.  Which  part  of  the  embryo  first  appears  above  ground  ? 
6.  What  is  the  shape  of  this  part  ? 

8.  Study  a  whole  seedling  at  this  stage  (see  7  above), 

from  which  one  cotyledon  has  been  removed. 

a.  Describe  the  changes  that  have  taken  place  in  each 

part  of  the  embryo  since  the  seed  began  to  sprout. 

b.  Describe  the  position  and  appearance  of  the  main  root 

and  its  branches  that  appear  in  this  stage. 

c.  Make  a  drawing,  natural  size,  of  a  seedling  at  this 

stage  and  show  by  a  horizontal  line  the  ground  level. 
Label  each  part. 

9.  Study  a  well-developed  seedling,  comparing  it  with  the 
stages  already  drawn,  and  answer  the  following 
questions : 

a.  What  changes  in  the  size  of  the  cotyledons  do  you 

notice  as  the  seedling  grows  older?  Most  of  the 
food  for  the  early  development  of  the  seedling  is 
furnished  by  the  cotyledons;  suggest,  therefore, 
the  cause  of  the  change  in  size  of  the  cotyledons, 
which  you  have  noticed. 

b.  What  parts  of  the  developing  embryo  have  changed  in 

color  during  germination;  how  have  they  changed? 


B  C 

FIG.  45.  —  Stages  in  the  development  of  the  squash  seedling.  —  (Bailey.) 


100 


PLANT  BIOLOGY 


c.   What  parts  of  the  oldest  seedling  have  developed  from 

the  plumule? 

10.  Draw  the  oldest  stage  of  the  bean  seedling,  and  label 
main  or  primary  root,  root-branches  or  secondary 
roots,  ground  level,  cotyledons  (or  scar  left  by  coty- 
ledons) ,'hypocotyl,  stem  above  cotyledons  (epicotyl), 
leaves,  terminal  bud. 

108.  Study  of  the  corn  seedling  and  its  development  from 
the  corn  grain.  —  Laboratory  Study  No.  52.  (Optional.) 

Materials:  Dry  and  soaked  corn  grains;  seedlings  of  various 
sizes  grown  as  described  above  for  the  bean  seedling.  Corn  grains 
should  be  planted  with  the  pointed  end  down. 

The  structure  of  the  corn  grain  and  the  development  of  the  corn 
embryo  can  be  understood  much  more  easily  if  the  study  of  the 
corn  seedling  is  made  first,  and  later  that  of  the  corn  grain. 

A.   Seedling  just  breaking  ground. 

1.  Examine  a  pot  of  seedlings  that  are  just  pushing  their 

way  through  the  soil  or  sawdust,  and  study  a 
seedling  of  this  stage  that  is 
given  you.  All  the  parts  of 
the  seedling  above  the  corn 
grain  have  developed  from 
the  first  bud  or  plumule. 

a.  What  is  the  shape  of  the  part  that 
first  breaks  through  the  soil? 

6.  Look  for  the  sheath  leaf  sur- 
rounding the  unfolding 
leaves,  and  trace  it  down  to 
the  ridge  around  the  stem 
from  which  it  springs.  How 
does  this  sheath  or  first  leaf 
of  the  plumule  differ  from 
the  unfolding  leaves?  What 
is  its  probable  use? 

2.  Observe  the  scar  on  the  grain,  showing  where  it  was 

fastened  to  the  cob,  and  notice  the  shape  of  the 


FIG.  46.  —  Wheat  Seedling. 


PLANT  PROPAGATION  101 

grain  at  its  opposite  end.  Does  the  plumule 
develop  from  the  blunt  end  or  the  pointed  end  ? 
3.  Make  a  sketch  of  the  seedling  (X  2)  and  label  grain  of 
corn,  scar  where  grain  was  attached  to  the  cob, 
stem  of  plumule,  sheath  leaf,  unfolding  leaf,  main 
root,  rootlets,  soil  line. 

B.  Cam  grain  just  sprouting. 

1.  Examine  a  corn  grain  that  has  just  sprouted.     Recall 

to  mind  the  end  of  the  grain  from  which  the  main 
root  grew.  (If  you  are  not  sure,  look  at  your 
drawing,  or  better  yet  the  seedling.) 

a.  What  part  of  the  little  corn  plant  breaks  through  the 

covering  first? 

b.  What  other  part  of  the  embryo  shows  signs  of  growth? 

2.  Remove  the  thin  covering  from  the  grain,  and  observe 

an  oval  body  embedded  in  the  corn  grain.  This  is 
the  little  corn  plant  or  embryo.  How  does  the 
embryo  differ  in  color  from  the  rest  of  the  grain? 

3.  The  oval-shaped  body  from  which  the  root  and  plumule 

seem  to  spring  in  the  grain  of  corn  is  called  the 
cotyledon.  The  remainder  of  the  grain  is  endo- 
sperm, which  is  the  food  material  for  the  develop- 
ment of  the  embryo.  Make  a  sketch  of  the  seed- 
ling at  this  stage  (X2)  and  label  single  cotyledon, 
plumule,  endosperm  or  food  material,  main  root. 

C.  Corn  grain. 

1.  Very  carefully  scrape  away  a  little  of  the  surface  of  the 

cotyledon  of  a  dry  or  soaked  grain  till  the  other 
parts  of  the  little  plant  or  embryo  come  into  view. 
Make  out  the  plumule  and  main  root. 
Sketch  the  corn  grain  and  label  cotyledon,  plumule, 
tiny  root,  food  material  around  the  plant  (endo- 
sperm). 

2.  Cut  a  corn  grain  in  such  a  way  as  to  divide  the  embryo 

and  endosperm  lengthwise  in  half.  Put  one  half  in 
iodine.  Where  in  the  corn  grain  is  starch  pres- 
ent? Where  is  it  absent? 


102  PLANT  BIOLOGY 

D.   Corn  seedling  well  advanced. 

1.  What  changes  have  taken  place  during  the  development 

of  the  seedling  in  the  roots?  in  the  plumule? 

2.  How  does  the  veining  of  the  leaves  in  the  corn  plant 

differ  from  that  in  the  leaves  of  the  bean  plant  ? 

3.  Where  do  you  find  aerial  or  air  roots  on  the  corn  seedling? 

(Roots  growing  above  ground  are  aerial  roots.) 

4.  Pinch  the  grain  between  your  fingers.     What  changes 

do  you  notice  in  the  amount  of  food  material?     How 
can  you  account  for  these  changes? 

5.  Make  a  sketch  of  the  seedling  and  label  corn  grain,  coty- 

ledon, stem,  leaves,  aerial  roots,  soil  roots. 

109.     Suggestions  for  growing  seedlings  at  home.      (Optional.) 

A.  Window  box.  —  Secure  a  wooden  box  at  least  six  inches  in 
depth,  and  of  a  convenient  size  to  place  in  front  of  a  south  window, 
if  you  have  such  a  window  at  home.     Nearly  fill  the  box  with  rich 
earth  which  has  been  finely  pulverized  or  sifted.     If  possible,  mix 
in  thoroughly  some  well- rotted  manure  and  a  tablespoonful  of  pre- 
pared fertilizer.     Soak  your  seeds  for  twenty-four  hours,  and  plant 
them  at  a  depth  equal  to  four  times  the  thickness  of  the  seeds. 
Cover  the  seeds  with  dirt,  press  it  down  firmly,  and  sprinkle  with 
water  till  the  earth  is  thoroughly  moistened  to  a  depth  of  at  least 
four  inches.     See  that  your  garden  is  kept  as  nearly  as  possible  at  a 
temperature  of  70  degrees.     Add  enough  water  day  by  day  to  keep 
the  ground  moist. 

B.  Tumbler  garden.  —  Secure  several  pieces  of   blotting  paper 
or  other  porous  paper,  and  cut  it  about  as  wide  as  the  tumbler  is 
high.     Wet  the  paper  and  roll  it  into  a  hollow  cylinder  that  fits 
inside  the  tumbler.     Between  the  blotting  paper  and  the  glass 
place  the  soaked  seeds  with  their  hilums  in  several  different  posi- 
tions.    Fill  the  interior  of  the  tumbler  with  wet  sawdust,  cotton,  or 
crumpled  paper.     Cover  the  tumbler  loosely  and  keep  the  contents 
moist,  and  at  a  temperature  of  about  70  degrees. 

C.  Glass-plate  garden.1  —  Secure  two  pieces  of  glass  about  5X7 

1  The  authors  are  indebted  to  Dr.  Cyrus  A.  King,  Head  of  Depart- 
ment of  Biology  of  Erasmus  Hall  High  School,  Brooklyn,  N.  Y.,  for 
this  method  of  germinating  seeds. 


PLANT  PROPAGATION 


103 


inches  (picture  negatives  cleaned  in  hot  water  are  admirable  for 
this  purpose).  Upon  one  of  the  glasses  put  a  layer  of  wet  cotton 
wadding  about  half  an  inch  thick.  Arrange  the  seeds  (which  have 
been  soaked  for  24  hours)  with  their  hilums  in  several  different 
positions,  and  place  on  top  of  them  the  second  plate  of  glass.  Tie 
strings  about  the  two  glasses,  and  stand  the  "garden"  in  about  an 
inch  of  water.  The  water  will  rise  between  the  glasses  and  keep  the 
developing  seedlings  moist.  After  the  seeds  have  begun  to  sprout, 
turn  the  " garden"  so  that  it  rests  on  another  edge,  and  note  the 
effect  on  direction  of  growth  of  the  hypocotyl. 


Observations  to  be  made  on  the  development  of  each  seed 

1.  What  part  of  the  seedling  first  appears  above  ground?     (Make 

drawings.) 

2.  Does  this  part  come  up  straight  or  in  the  form  of  an  arch  ? 

3.  What  kind  of  veining  is  found  in  the  leaves  ? 

4.  How  many  cotyledons  are  present,  and  what  is  their  use  ? 

5.  In  what  direction  does  the  main  root  tend  to  grow  ?  the  sec- 

ondary roots  ? 

110.  Comparison  of  seeds  and  seedlings.  —  Study  No.  53. 
(Optional.) 

Soak  and  plant  at  home  as  directed  under  Materials  (107), 
several  kinds  of  seeds.  Study  the  seeds  and  seedlings,  and  fill  out 
in  your  note-book  a  table  like  the  following : 


BEAN 

PEA 

SQUASH 

CORN,  ETC. 

Number  of  cotyledons  .     .     .'. 

Position  of  stored  food  .     .     . 

Kinds  of  food  present    .     .     . 

104 


PLANT  BIOLOGY 


Function  of  cotyledons      .     . 

(Storage  of  food)  .... 

fTjY>l  lacrp^ 

Method  of  breaking  ground   . 

(By  arched  plumule) 

(By  erect  pointed  plumule) 

Veining  of  foliage  leaves    .     . 
fNpffpH^ 

/pQT,Qii0n 

\i:  aranei;      

111.  Nutrients  stored  in  corn  grains  for  the  use  of  the  seedling. 
—  Laboratory  Study  No.  54.  (Optional.) 

Grind  with  a  mortar  and  pestle  some  corn  grains  till  a  fine  meal 
is  prepared.  Test  for  each  of  the  food  substances  and  fill  out  in 
your  note-book  a  table  like  the  following : 


NAME  OP  NUTRIENT 

CHEMICAL  USED 

RESULT 

CONCLUSION 

Starch  .  .  . 
Grape  sugar  . 
Protein  .  .  . 
Fat  l  .  .  .  . 

112.  Of  what  importance  is  the  endosperm  in  the  develop- 
ment of  corn  seedlings  ?  —  Laboratory  Study  No.  55.  Home 
work  or  demonstration. 

Soak  twenty-four  or  more  corn  grains  over  night.  Care- 
fully remove  from  half  of  them  all  the  endosperm  (food 

1  To  test  for  fat,  put  some  of  the  cornmeal  into  a  test  tube,  add 
some  ether,  shake  frequently,  and  let  the  tube  stand  for  a  time.  At 
the  end  of  twenty-four  hours  pour  off  the  clear  liquid  upon  pieces  o'f 
glazed  paper.  After  the  ether  has  evaporated,  hold  the  paper  to 
the  light.  Be  careful  not  to  hold  the  ether  near  a  flame. 


PLANT  PROPAGATION 


105 


materials)  from  around  the  embryo  corn  plant.  Plant  the 
corn  grains  and  the  corn  embryos  in  rich  soil,  covering  both 
with  the  same  depth  of  earth,  and  marking  the  location  of  the 
two  sets.  Put  them  in  a  warm  place. 

1.  Describe  the  preparation  of  the  experiment. 

2.  At  the  end  of  two  weeks  state  the  number  of  each  group  of 

seedlings  that  have  pushed  through  the  soil. 

3.  What  difference  in  the  size  of  the  two  sets  of  seedlings  do 

you  notice  at  the  end  of  two  weeks?    at  the  end  of 
three  weeks? 

4.  What  has  this  experiment  taught  you  ? 

II.   OTHER  METHODS  OF  PLANT  PROPAGATION 

113.  Grafting.  —  The  method  often  adopted  by  fruit  growers 
to  produce  new  and  better  varieties  is  that  known  as  grafting. 
This  method  of  plant  propa- 
gation may  be  carried  on  in 
the  following  manner.  A 
young  shoot,  known  as  the 
scion  (Fig.  47,  A,  6),  is  cut 


FIG.  47.  —  Methods  of  grafting. 

in  an  oblique  direction  from  a  tree,  the  fruit  of  which  is  desired, 
and  a  similar  oblique  cut  is  made  across  the  twig  of  another  tree, 
called  the  stock  (Fig.  47,  A ,  a) ,  of  a  related  kind.  The  two  freshly  cut 
surfaces  are  then  closely  applied  to  each  other,  and  the  scion  and 


106  PLANT  BIOLOGY 

stock  are  bound  together  by  grafting  wax  (Fig.  47,  B,c},  which  is  put 
around  the  outer  bark  to  hold  the  two  pieces  in  place  and  to  pre- 
vent evaporation.  In  this  way  the  cambium  layers  of  the  two 
plants  are  brought  into  close  contact  and  soon  unite.  The  ducts  of 
the  stock  likewise  join  those  of  the  scion,  and  so  sap  is  transmitted 
to  the  grafted  twig,  which  grows  and  develops  its  fruit  as  though  it 
were  still  a  part  of  the  plant  from  which  it  was  taken.  There  are 
many  different  ways  of  cutting  and  binding  the  twigs  together, 
and  even  buds  may  be  used  as  scions  (Fig.  47,  C,  b).  But  the  prin- 
ciple is  the  same  in  every  case. 

Grafting  is  of  necessity  employed  in  producing  new  plants  of 
seedless  grapes  or  oranges.  It  is  also  frequently  adopted  to  com- 
bine the  desirable  characteristics  of  two  different  plants.  For 
example,  when  the  vineyards  of  France  were  being  destroyed  by 
an  insect  that  attacked  the  roots,  the  fruit-growers  overcame  the 
difficulty  by  grafting  the  wine-producing  scions  upon  the  more  vigor- 
ous and  resistant  nutritive  stock  of  grapevines  introduced  from 
America. 

114.  Slips,  runners,  and  layers.  —  Another  method  of  producing 
new  plants  is  that  of  cutting  twigs  of  plants  that  are  desired,  and 


FIG.  48.  —  Strawberry  plant  with  runner.  —  (Bailey.) 

placing  the  lower  end  of  the  stems  in  moist  sand.  Roots  soon 
develop  on  these  so-called  slips,  and  the  new  plants  thus  formed  can 
then  be  transplanted  into  good  rich  soil.  Any  one  who  has  seen  a 
vigorous  strawberry  plant  knows  that  it  sends  out  a  lot  of  slender 
stems  which  grow  so  rapidly  that  they  are  known  as  runners.  When 
a  portion  of  one  of  these  runners  lies  upon  the  surface  of  moist  soil, 


PLANT  PROPAGATION 


107 


roots  are  formed  as  in  the  case  of  slips,  and  when  they  are  firmly 
established,  the  connection  with  the  parent  plant  may  be  severed, 
and  thus  a  new  strawberry  plant  secured.  Still  another  method 
of  propagating  plants  is  known  as  layering,  which  may  be  accom- 
plished in  raspberry  or  blackberry  plants  by  burying  the  tips  of 
branches  in  the  soil,  thus  inducing  the  production  of  roots.  The 
new  plant  can  then  be  severed  from  the  parent. 

115.   Tubers.  —  New  potato  plants  are  commonly  secured,  not 
by  planting  potato  seeds,  but  by  cutting  into  pieces  a  potato  which 


FIG.  49.  —  Potato  plant  and   tubers  grown  from  dark   colored  potato  in 
center.  —  (U.  S.  Dept.  Agriculture.) 

is  a  fleshy  underground  stem  or  tuber,  each  piece  having  one  or  more 
"eyes,"  and  putting  these  into  the  ground.  In  each  eye  is  a  bud, 
and  when  this  sprouts  it  develops  stems  and  leaves  above  ground, 
the  new  plant  thus  formed  getting  a  considerable  amount  of 
nutrition  from  the  food  stored  in  the  tuber  during  the  preceding 
season. 


108  PLANT  BIOLOGY 

116.  Bulbs.  —  Still  another  method  of   propagating  plants  is 
by  means  of  bulbs,  which,  in  the  onion,  for  example,  consist  of  a  short, 
thickened  underground  stem,  to  which  are  attached  many  layers 
of  thickened  parts  of  leaves  known  as  bulb-scales.     Frequently,  as 
in  the  tulip  and  hyacinth,  after  the  food  stored  in  the  bulb  has  been 
used  in  the  early  spring  to  develop  stem,  leaves,  and  flowers,  the 
nutritive  organs  store  away  food  for  another  season  by  producing 
new  bulbs  close  to  the  old  one. 

117.  Home  bulb  culture.  —  (Optional.) 

Few  plants  are  easier  to  cultivate  or  give  greater  satisfaction, 
especially  in  winter,  than  those  that  grow  from  bulbs.  Secure  a  few 
tulip,  hyacinth,  or  narcissus  bulbs  and  bury  them  in  pots  of  rich 
earth.  Water  them  well  and  put  them  in  a  dark,  cool  place  for  four 
to  six  weeks,  until  the  roots  appear  through  the  opening  at  the  bot- 
tom of  the  pot.  Then  put  them  in  a  warm,  sunny  place,  keep  them 
well  watered,  and  the  flowers  will  appear  in  a  few  weeks. 

III.   CONDITIONS  THAT  ARE   ESSENTIAL  FOR  THE  GROWTH 

OF  PLANTS 

118.  The  five  essential  conditions  for  plant  growth  are  the 
following :    (1)  moisture,  (2)  favorable  temperature,  (3)  air, 
(4)  light,  (5)  food.     We  have  already  shown  the  necessity  of 
air  for  the  germination  of  seeds  (79)  and  for  the  liberation  of 
energy  (76).     The  use  of  the  food  stored  in  the  corn  grain 
for  the  corn  embryo  was  also  demonstrated  in  112.     We  have 
also  proved  that  green  plants  do  not  manufacture  carbohy- 
drates in  the  absence  of  sunlight  (30) .     We  can  likewise  show 
experimentally  the  relation  of  moisture  and  temperature  to 
the  germination  of  seeds  and  to  the  growth  of  plants. 

119.  Relation  of  moisture   to   germination  and  growth.  —  Labo- 
ratory Study  No.  56.     (Optional.)     Suggested  as  home  work. 

Secure  three  tumblers  of  same  size  (tin  covered  jelly-tumblers  are 
very  satisfactory).     In  the  bottom  of  each  put  a  piece  of 


PLANT  PROPAGATION  109 

sponge  about  half  the  size  of  the  fist  (a  wad  of  cotton  or  paper 
will  answer).  Label  the  first  tumbler  No.  1,  and  place  upon 
the  sponge  10  pea  seeds  that  have  been  soaked  for  24  hours. 
In  the  second  tumbler  (labeled  No.  2)  put  10  soaked  peas,  and 
add  enough  water  to  come  nearly  to  the  top  of  the  sponge. 
Put  10  soaked  pea  seeds  into  the  other  tumbler  (No.  3),  and 
add  sufficient  water  to  cover  all  the  peas.  To  prevent  the 
evaporation  of  the  water,  cover  the  three  tumblers,  and  place 
them  side  by  side  in  a  moderately  warm  temperature  (65°- 
70°  F.),  and  label  each  "  Please  do  not  disturb." 

1.  Which  one  of  the  five  conditions  (enumerated  in  118  above)  is 

different  for  the  three  groups  of  seeds  ? 

2.  Name  all  of  these  conditions  which  are  practically  the  same  for 

the  seeds  in  all  three  of  the  tumblers. 

3.  At  the  end  of  a  few  days  compare  the  seeds  in  the  three  tum- 

blers. What  percentage  of  the  seeds  in  each  of  the  three  tum- 
blers has  germinated  ? 

4.  State  clearly  your  conclusion  as  to  the  relation  of  water  to  the 

germination  of  pea  seeds. 

5.  Allow  the  three  tumblers  to  stand  side  by  side  in  a  warm,  light 

place  for  several  weeks.  Describe  the  changes  that  take  place 
in  each  tumbler,  and  state  your  conclusion  as  to  the  relation 
of  moisture  to  the  growth  of  pea  plants. 

120.   Relation  of  temperature  to  germination  and  growth.  —  Labo- 
ratory Study  No.  57.     (Optional.)     Suggested  as  home  work. 

Prepare  three  tumblers  with  sponges  (cotton  or  paper)  as  in  119 
above,  putting  in  water  enough  to  come  nearly  to  the  top  of 
the  sponge  in  each  dish.  In  each  tumbler  place  10  soaked 
peas,  and  put  on  the  covers.  Label  No.  1,  No.  2,  and  No.  3. 
Set  tumbler  No.  1  in  the  refrigerator  or  in  some  place  where 
it  will  not  freeze.  Keep  Tumbler  No.  2  at  the  temperature 
of  the  living  room.  Place  No.  3  where  the  temperature  is 
over  100°.  Make  sure  that  all  tumblers  have  about  the 
same  amount  of  light  by  covering  each  with  black  paper  or  a 
cloth.  By  the  aid  of  a  thermometer  find  and  record  the  tern- 


110  PLANT  BIOLOGY 

•  perature  of  each  place  where  you  put  a  tumbler.  Each  day 
look  at  the  tumblers,  and  if  necessary  add  enough  water  to 
keep  the  level  the  same  in  all  three. 

1.  Which  one  of  the  five  conditions  named  in  118  is  different  for 

the  three  groups  of  seeds  ? 

2.  Name  all  the  conditions  which  are  practically  the  same  for  the 

seeds  in  all  three  of  the  tumblers. 

3.  At  the  end  of  a  few  days  compare  the  seeds  in  the  three  tumblers. 

What  percentage  of  the  seeds  in  each  of  the  three  tumblers 
has  germinated  ? 

4.  State  clearly  your  conclusion  as  to  the  relation  of  temperature  to 

the  germination  of  pea  seeds. 

5.  Allow  the  three  tumblers  to  stand  in  the  three  different  tem- 

peratures for  several  weeks.  Describe  the  changes  that  take 
place  in  each  tumbler,  and  state  your  conclusion  as  to  the 
relation  of  temperature  to  the  growth  of  pea  plants. 

121.  The  soil.  —  "  From  the  soil  all  things  come ;  and 
into  it  all  things  at  last  return ;  and  yet  it  is  always  new,  and 
fresh,  and  clean,  and  always  ready  for  new  generations.  This 
soft,  thin  crust  of  the  earth  —  so  infinitesimally  thin  that  it 
cannot  be  shown  in  proper  scale  on  any  globe  or  chart  —  sup- 
ports all  the  countless  myriads  of  men,  and  animals,  and 
plants,  and  has  supported  them  for  countless  cycles,  and  will 
yet  support  for  other  countless  cycles.  In  view  of  this 
achievement,  it  is  not  strange  that  we  do  not  yet  know  the 
soil  and  understand  it ;  and  we  are  in  a  mood 'to  be  patient 
with  our  shortcomings."  1 

Even  a  casual  examination  of  the  soil  in  any  region  shows  that 
it  has  a  complex  structure.  Usually  it  is  composed  of  some  coarse 
.particles  known  as  gravel,  finer  grains  called  sand,  and  still  more 
minute  ingredients,  the  mud  or  clay.  The  relative  proportions  of 
these  constituents  determine  whether  the  soil  is  a  gravelly  soil,  a 
sandy  soil,  or  a  clayey  soil.  The  soil  particles  to  which  we  have 

1  Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  I, "  Farms,'* 
p.  323. 


PLANT  PROPAGATION  111 

referred  supply  the  mineral  ingredients  needed  by  plants  in  the  form 
of  soil- water.  But  soil,  to  be  fertile,  must  contain  a  considerable 
quantity  of  vegetable  mold,  the  so-called  humus,  a  dark  brown  or 
black  substance  produced  by  the  decay  of  vegetable  matter.  This 
is  the  reason  that  florists  mix  with  the  dirt  in  their  flower-pots  a 
handful  of  material  obtained  from  the  floor  of  the  forest  (see 
frontispiece),  where  leaves  have  fallen  and  decomposed  year  after 
year. 

122.  Moisture.  —  If  the  student  has  tried  the  experiment  in 
119,  he  will  have  been  convinced  that  the  amount  of  moisture 
supplied  to  seeds  or  plants  has  a  great  deal  to  do  with  their  develop- 
ment.    Soils  in  very  dry  or  arid  regions   are  deficient  in  water, 
and  this  must  be  supplied  by  irrigation.     In  semiarid  regions  proper 
methods  of  tillage,  as  we  shall  see,  will  do  much  to  keep  the  soil 
in  a  proper  condition  for  plant  growth,  so  far  as  moisture  is  con- 
cerned.   Very  moist  or  "heavy"  soils,  on  the  other  hand,   are 
unfavorable  for  the  growth  of  most  plants,  and  so  the  excess  of  water 
must  be  removed  by  drainage. 

Reviewing  some  of  ifhe  facts  already  learned,  we  see  that  a  large 
supply  of  water  must  be  secured  by  plants  from  the  soil,  because  — 

"1.  A  living  plant  contains  a  large  proportion  of  water  —  gen- 
erally more  than  75  per  cent  of  its  weight. 

"2.  Large  quantities  of  water  must  pass  through  the  plant  in 
order  that  the  food  solution  in  the  soil  may  be  carried  to  the  leaves, 
and  the  substances  that  it  contains  may  be  converted  into  organic 
matter.  This  water  loss  takes  place  by  transpiration  from  the 
leaves  and  growing  shoots. 

"Careful  and  extended  experiments  in  this  country  and  Europe 
have  shown  that  300  to  500  tons  of  water  are  taken  from  the  soil 
by  the  various  crops  for  each  ton  of  dry  substance  produced."  1 

123.  Relation  of  the  soil  to  air.  —  When  the  interstitial  spaces 
between  the  particles  of  soil  are  not  filled  with  water,  or  when  they 
are  only  partly  filled,  they  contain  air.    The  air  which  circulates  in 

1  Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  I, "  Farms." 
p.  353. 


112  PLANT  BIOLOGY 

the  soil  differs  in  composition  from  the  air  above  the  surface.  As  a 
rule,  the  soil  air  contains  less  oxygen  and  more  carbonic  acid  (CO2), 
ammonia,  and  vapor  of  water.  The  increased  amount  of  carbonic 
acid  and  ammonia  have  their  origin  in  the  organic  matter  or  humus. 
A  soil  is  not  in  the  best  condition  for  the  production  of  crops  unless 
there  is  within  its  depths  a  free  circulation  of  air.  This  is  true 
because  oxygen  in  the  soil  is  as  essential  for  the  life  of  the  plant  as 
it  is  for  the  animal.  .  .  . 

"When  the  soil  is  full  of  water  to  within  a  few  inches  of  the  sur- 
face, there  can  be  no  circulation  of  air  among  its  particles.  Ade- 
quate ventilation  can  be  provided  for  such  a  soil  only  by  drainage. 
Drainage  ventilates  the  soil  by  lowering  the  ground  water  three  or 
four  feet,  and  thus  makes  it  possible  for  the  roots  of  plants  to  pene- 
trate soil  more  deeply.  In  time  these  roots  die  and  decay  and 
afford  passageways  throughout  the  soil  for  the  ready  movement 
of  the  air."  * 

124.  Relation  of  soil  to  heat.  —  The  influence  of  the  tempera- 
ture of  the  soil  on  crop  production  is  a  factor  of  considerable 
importance.  The  life  processes  of  a  plant  are  practically  suspended 
below  a  certain  minimum  temperature,  which  is  about  40  degrees 
Fahrenheit  for  most  cultivated  crops.  Above  this  temperature 
all  the  vital  activities,  as  germination  and  growth,  increase  until 
the  optimum  is  reached.  Above  this  point  these  life  processes  de- 
crease in  activity  until  the  point  is  reached  when  they  cease.  The 
soil  is  a  great  factory  that  has  its  production  vastly  increased  as 
the  temperature  rises.  .  .  .  The  minimum  temperature  at  which 
corn  germinates  and  also  the  minimum  for  its  growth  is  48°  or 
49°  F.  Its  optimum  is  about  93°  F.  ... 

"The  sources  of  the  heat  of  the  soil  are  the  internal  heat  of  the 
earth,  the  sun,  and  decaying  vegetable  matter.  It  is  difficult  to 
estimate  to  just  what  extent  the  internal  heat  of  the  earth,  which 
itself  is  very  great,  affects  the  temperature  near  the  surface  of  the 
earth.  However,  the  amount  of  heat  from  this  source  is  insignificant, 
is  a  constant  factor,  and  is  entirely  beyond  the  control  of  man. 

1  Bailey's  "Cyclopedia  of  Agriculture,"  Vol.  IX,  "Farms,"  p.  357. 


PLANT  PROPAGATION  113 

Decaying  organic  matter  furnishes  some  heat  to  the  soil.  For 
example,  manure  heats  the  soil  to  a  limited  extent  when  it  is  spread 
on  the  surface  and  plowed  in.  ...  The  sun  is  by  far  the  most 
important  source  of  heat  for  the  soil.  When  its  rays  are  nearly 
vertical  there  is  tropical  heat ;  when  its  rays  are  withheld,  the  land 
is  locked  in  snow  and  ice.  The  heat  received  at  the  surface  passes 
downward  by  conduction."  1 

125.  Cultivation  of  the  soil.  —  A  moment's  thought  will 
conyince  us  that  since  all  the  food  of  man  is  ultimately  de- 
rived from  plants,  any  measures  that  tend  to  improve  crops 
and  reduce  the  cost  of  crop 
production  are  of  vital  in- 
terest to  all  of  us.  In  the 
past,  before  much  was 
known  in  regard  to  scien- 
tific principles,  farmers 
put  their  seeds  in  the 
ground,  cultivated  them 

relatively  little,  and  trusted  Nature  to  do  the  rest.  In 
recent  times,  however,  man  has  learned  a  great  deal  in 
regard  to  soils,  crops,  and  methods  of  cultivation,  so  that 
the  modern  farmer  is  often  able  to  double  the  yield  of  a 
given  area.  The  investigations  of  the  National  and  State 
Departments  of  Agriculture  have  done  much  to  make  farm- 
ing a  science,  and  the  future  will  doubtless  see  far  greater 
improvements. 

For  the  cultivation  of  plants  the  first  requisite  is  a  suitable 
preparation  of  the  soil.  This  involves,  in  the  first  place, 
plowing,  which  turns  under  any  weeds  or  other  plants  that 
may  have  grown  there  before  and  which  prepares  for  the  work 
of  the  harrow,  an  implement  which  pulverizes  the  soil  so  that 

1  Bailey's  "Cyclopedia  of  American  Agriculture,"  Vol.  I,  "Farms," 
pp.  355,  356. 


114  PLANT  BIOLOGY 

ready  penetration  of  the  roots  of  the  growing  plant  is  possible. 
In  small  garden  plots  this  work  is  done  by  the  use  of  spades, 
hoes,  and  rakes.  It  is  often  found  necessary  to  add  well- 
rotted  manures  to  increase  the  humus  of  the  soil  and  chemi- 
cally prepared  fertilizers,  which  furnish  available  mineral 

food  for  the  crops.  We 
have  already  called  at- 
tention to  the  necessity 
of  proper  drainage  of 
the  soil  before  crops  are 
planted  (122).  Scien- 
tific investigation  has 
demonstrated,  too,  that 
frequent  and  thorough 

stirring  of  the  soil  is  most  important  not  only  to  prevent 
the  growth  of  weeds,  but  also,  and  this  is  even  more 
essential,  to  conserve  the  soil  moisture,  and  insure  proper 
aeration  of  the  roots.  It  has  been  found  that  it  is  possible 
to  produce  large  crops  on  semiarid  land  if  the  top-surface  of 
the  ground  is  kept  in  a  thoroughly  pulverized  condition. 
This  is  the  so-called  method  of  "  dry  farming." 

L 

IV.   THE  STRUGGLE  FOR  EXISTENCE  AND  ITS  EFFECTS 

126.  Variation  among  plants.  —  We  have  all  heard  the  common 
expression  "as  nearly  alike  as  two  peas."  In  reality,  however, 
if  our  powers  of  observation  were  sharp  enough,  we  should  probably 
find  that  no  two  peas  are  exactly  alike  in  shape,  color,  size,  and 
weight.  The  plants  grown  side  by  side  from  any  two  peas  would 
also  vary  in  height,  in  number  and  position  of  leaves,  and  in  the 
number  and  vigor  of  flowers  and  seeds.  In  other  words,  as  every 
human  being  has  certain  distinguishing  characteristics,  so,  too,  we 
should  bear  in  mind  that  every  individual  plant,  however  small, 
shows  certain  differences  or  variations  from  every  other  individual 
of  its  class. 


PLANT  PROPAGATION 


115 


127.  The  numbers  of  seeds  produced  by  plants.  —  A  second  fact 
which  is  evident  to  all  is  that  plants  produce  an  enormous  number 
of  seeds.  Suppose  we  consider  the  case  of  a  vigorous  pea-vine.  In 
the  course  of  a  season  it  should  produce  at  least  20  pods,  each  con- 
taining at  least  5  seeds.  Hence,  at  the  end  of  a  single  season,  one 
pea  seed  would,  if  conditions  were  favorable,  have  multiplied  itself 
100  times.  If  each  one  of  these  seeds  were  to  be  planted  where  it 


FIG.  52.  —  Variations  in  the  corn  ears  produced  in  a  single  field.  —  (Courtesy 
of  Dr.  E.  M.  East,  Bussey  Institution,  Harvard  University.) 

had  plenty  of  moisture,  light,  food,  air,  and  favorable  temperature, 
it  likewise  should  give  rise  to  100  seeds,  and  so  at  the  end  of  the 
second  season  we  ought  to  have  100  X  100,  or  10,000  pea  seeds,  all 
propagated  from  a  single  pea  seed.  Simple  multiplication  shows  us 
that  at  the  end  of  five  years  a  moderately  prolific  plant  like  the- 
garden  pea  would  have  given  rise,  had  all  conditions  been  favor- 
able to  10,000,000,000  new  seeds.  Bergen  has  made  a  patient 
count  of  the  number  of  seeds  produced  by  an  average  morning 
glory  plant,  and  finds  it  to  be  rather  more  than  3000;  hence, 
at  the  end  of  the  fifth  year,  if  such  a  rate  of  reproduction  were 


116  PLANT  BIOLOGY 

to  be  continued,  there  would  be  243,000,000,000,000,000  morning 
glory  seeds.1 

It  is  evident,  however,  that  no  pea  vine  or  morning  glory  plant, 
if  left  to  itself,  would  be  able  to  produce  anything  like  the  number 
of  seeds  we  have  named,  for  otherwise  at  the  end  of  a  short  term  of 
years  there  would  not  be  room  on  the  whole  surface  of  the  globe  for 
any  other  kinds  of  plants  than  these.  As  a  matter  of  fact,  the  num- 
ber of  individuals  of  a  given  kind  of  organism  does  not  vary  much 
from  year  to  year.  In  the  first  place,  many  seeds  are  eaten  by  birds 
and  other  animals.  Again,  many  other  seeds  are  not  carried  to  a 
place  where  they  find  all  the  conditions  that  are  essential  for  germi- 
nation (118).  Still  other  seeds,  even  if  planted  in  good  soil 
and  in  favorable  surroundings,  fail  to  germinate.  Because  of  the 
great  losses  of  seeds  in  one  or  the  other  of  these  three  ways,  we  can 
get  some  idea  of  the  reason  why  plants  must  produce  a  great  abun- 
dance of  seeds  if  their  kind  is  to  be  perpetuated. 

128.  The  struggle  for  existence  among  plants.  —  But  even  if 
seeds  finally  germinate  and  get  a  foothold  on  the  soil,  a  great  many 


FIG.  53.  —  The  struggle  for  existence  and  the  survival  of  the  fittest  among 

turnips. 

of  the  plants  thus  started  will  never  reach  maturity  and  ripen  their 
seeds.     In  the  first  place,  each  plant  is  struggling  to  lift  up  its  leaves 

1  See  Bergen's  "Essentials  of  Botany"  (1910),  p.  202. 


PLANT  PROPAGATION  117 

to  the  light  and  air,  and  those  that  are  most  vigorous  usually  get 
above  and  shade  the  others.  Again,  the  supply  of  water  and  mineral 
food  in  the  soil  of  a  given  area  is  limited ;  hence,  plants  that  cannot 
get  what  they  need  are  dwarfed  and  finally  starved  to  death.  In 


FIG.  54.  —  Charles  Darwin. 

the  third  place,  injurious  insects  destroy  an  enormous  amount  of 
vegetation,  the  loss  of  cultivated  crops  alone  from  this  cause  being 
estimated  at  $700,000,000  annually.  Frosts,  dry  seasons,  heavy 
rains,  and  fungous  diseases  are  other  important  factors  in  the  life 
of  many  plants.  And  so  if  we  were  able  to  see  what  is  actually 
going  on  in  each  square  foot  of  the  earth's  surface,  whether  of  forest, 


118 


PLANT  BIOLOGY 


field,  or  meadow,  we  should  doubtless  witness  a  life  and  death 
struggle  for  existence  (1)  between  individual  plants,  of  the  same 
kind,  (2)  between  individual  plants  of  different  kinds,  and  (3)  be- 
tween plants  and  animals. 

Charles  Darwin  in  his  great  book  on  the  "Origin  of  Species," 
published  in  1859,  —  a  book  which  has  doubtless  influenced  human 
thought  more  than  any  other  book  of  modern  times,  —  closes  his 
chapter  on  the  "Struggle  for  Existence"  with  the  following  words: 
"When  we  reflect  on  this  struggle  we  may  console  ourselves  with  the 
full  belief  that  the  war  of  nature  is  not  incessant,  that  no  fear  is 

felt,  that  death  is  gen- 
erally prompt,  and  that 
the  vigorous,  the 
healthy,  and  the  happy 
survive  and  multiply."1 

129.  The  survival  of 
the  fittest. —  We  have 
'seen  in  our  study  thus 
far  (1)  that  no  two  in- 
dividual plants  even  of 
the  same  kind  are  ex- 
actly alike,  (2)  that 
enormous  numbers  of 
seeds  are  produced  by 
plants,  and  (3)  that 
there  is  inevitable  com- 
petition or  struggle  for 
existence.  The  ques- 
tion, then,  that  con- 
fronts us  is  this :  Which 
of  the  many  competi- 
tors will  survive  in  the 
struggle,  reach  maturity,  and  finally  reproduce  themselves  ?  Obvi- 
ously those  individual  plants  that  vary  from  the  rest  in  such  a 


FIG.  55.  —  Dandelion  plant.  —  (Bailey.) 


1  Darwin's  "  Origin  of  Species,"  p.  72. 


PLANT  PROPAGATION  119 

way  that  they  can  best  adapt  themselves  to  their  surroundings. 
Let  us  see,  for  instance,  why  certain  weeds  like  the  dandelion  are 
so  common  a  nuisance  on  our  lawns.  In  the  first  place  these 
weeds  have  fleshy  roots  that  reach  deep  down  into  the  soil,  thus 
helping  the  plant  to  get  and  keep  a  stock  of  moisture  and  food. 
In  the  second  place  the  reserve  supply  of  nutrition  stored  in 
these  roots  enables  the  plants  to  put  forth  leaves  and  flowers  in 
early  spring,  and  so  to  get  a  good  start  ahead  of  their  com- 
petitors. Again,  their  short  stems  and  tough  leaves  can  be 
trampled  upon  without  killing  the  plant.  Insects  and  fungous 
diseases,  for  some  reason,  do  not  seem  to  attack  them.  And 
finally  dandelions  produce  a  large  number  of  tiny  seed-like 
fruits,  each  one  of  which  is  provided  with  a  delicate  tuft  of  hair 
which  a  puff  of  wind  will  carry  for  a  considerable  distance,  thus 
insuring  a  wide  dispersal  of  its  seeds.  In  nature,  then,  plants  like 
the  dandelion,  pigweed,  and  thistle  have  survived  in  the  struggle 
for  existence,  because  they  are  best  fitted  to  their  surroundings. 

V.  THE  IMPROVEMENT  OF  PLANTS  BY  MAN 

130.  Artificial  selection  of  favorable  variations.  —  In  the  pre- 
ceding pages  attention  was  frequently  called  to  the  fact  that  plants 
show  a  tendency  to  vary  more  or  less  from  each  other.  Now  it 
has  been  found  that  in  a  state  of  cultivation  this  tendency  becomes 
even  more  pronounced.  A  watchful  farmer  will  often  find  that  in 
his  cornfield  one  group  of  individuals  ripens  sooner  than  the  rest, 
and  so  if  he  wishes  to  sell  earlier  corn,  he  selects  and  plants  next  year 
corn  grains  derived  from  plants  that  have  varied  in  this  direction. 
Again,  he  may  notice  that  the  ears  on  certain  stalks  are  larger  and 
ripen  more  kernels  (see  Fig.  52) ;  these  the  crop-raiser  who  uses  his 
brains  would  select  for  seed  in  order  to  increase  his  yield  per  acre. 
Variations  in  many  other  directions  might  be  chosen  by  the  success- 
ful farmer  which  would  add  immensely  to  the  value  of  his  crops. 
It  is  estimated  that  if  every  farmer  were  to  select  his  seed  carefully, 
the  corn  production  in  the  United  States,  which  at  present  is  about 
$1,000,000,000,  in  a  short  time  would  be  increased  10  per  cent,  which 
would  add  $100,000,000  to  our  annual  income. 


120 


PLANT  BIOLOGY 


131.  Artificial  crossing  of  related  species.  —  Not  only  can  man 
secure  new  varieties  of  plants  by  watching  for  favorable  variations 
and  perpetuating  them  from  year  to  year,  but  he  can  actually  be 
instrumental  in  producing  new  kinds  of  plants.  This  process  is 
known  as  plant  breeding.  It  depends  fundamentally  on  the  prin- 
ciples we  learned  in  treating  of  cross-pollination  in  flowers.  Let 
us  illustrate  plant  breeding  by  the  following  account  of  the  work 
which  has  been  done  for  the  U.  S.  Department  of  Agriculture  by 
Dr.  H.  J.  Webber  of  Cornell  University.1 

In  the  winter  of  1894-1895  a  heavy  frost  destroyed  practically 
every  orange  tree  in  the  northern  and  central  part  of  the  State 

of  Florida.  The  loss  was  over 
$75,000,000.  The  problem  that 
confronted  the  orange  growers 
of  the  State  was  that  of  start- 
ing their  groves  anew  and  if 
possible  of  preventing  a  repeti- 
tion of  such  an  experience  by 
planting  a  more  hardy  kind  of 
orange  tree.  Dr.  Webber,  in 
casting  about  for  such  orange 
trees,  finally  chose  a  type  called 
the  trifoliate  orange  (Fig.  56) 
often  used  for  an  ornamental 
shrub,  and  one  that  would  not 
be  killed  by  winters  as  far  north 
as  Philadelphia.  The  fruit  of 
this  tree,  however,  is  small,  bitter, 
and  worthless  for  eating  pur- 
poses. His  task,  therefore,  was 
^^  to  combine  the  characteristics  of 

a  juicy,  sweet-flavored  fruit  of  the  ordinary  Florida  orange  tree 
with  the  hardy,  cold-resistant  character  of  the  trifoliate  type.  He 
proceeded  in  this  fashion: 

1  See  Year-books  of  U.  S.  Department  of  Agriculture,  1904,  1905, 
1906. 


FIG.    56.    —   Spray    from    trifoliate 
orange,  showing  leaves  and  fruit. 


PLANT  PROPAGATION 


121 


From  the  flower-buds  of  one  type  of  orange  trees  he  removed  all 
the  stamens  before  blossoming  time,  and  then  covered  the  pistils 
with  paper  bags  to  prevent  the  visit  of  insects  bringing  pollen.  A 
second  set  of  buds  on  trees  of  the  other  type  were  likewise  covered 
with  paper  bags  to  prevent  possible  mixing  of  pollen  by  insect  visi- 
tors. When  the  stamens  of  one  kind  of  orange  blossoms  and  the 


(Ufa     ^fc, 

767  77Z 


FIG.  57.  —  Fruits  of  two  parent  plants  (orange  and  trifoliate)  at  left.  Six 
types  of  hybrid  fruits  (Rusk,  Willits,  783,  771,  772,  767)  developed 
by  cross-pollination  from  the  parent  plants,  all  being  good  fruits  except 
767,  which  proved  to  be  worthless.  Compare  seeds  and  pulp  in  various 
sections. 

pistils  of  the  other  kind  had  matured,  the  bags  were  carefully 
removed,  and  the  pollen  of  one  variety  was  dusted  over  the  pistil 
of  the  other  (see  87).  The  paper  bag  was  then  replaced  over 
the  artificially  pollinated  pistil,  and  the  latter  left  to  ripen.  Fruits 


122 


PLANT  BIOLOGY 


formed  by  the  cross-pollination  of  two  different  kinds  of  plants  are 
known  as  hybrid  fruits.  The  orange  hybrid  fruits  thus  developed 
were  sent  to  Washington,  where  the  seeds  were  removed  and  planted 
in  greenhouses.  When  the  young  hybrid  trees  were  about  a  foot 
high,  they  were  sent  to  Florida  and  grown  in  a  garden  of  the  Depart- 
ment of  Agriculture. 

After  a  great  many  experiments  in  crossing  the  two  kinds  of 
oranges,  and  after  rejecting  hundreds  of  plants  that  proved  to  be 
worthless,  Dr.  Webber  has  succeeded  in  producing  a  type  of  tree  that 
will  withstand  the  winters  of  regions  from  three  hundred  to  four 
hundred  miles  north  of  the  present  orange-growing  section  of  Flor- 
ida, and  which  will  also  produce  a  valuable,  juicy  fruit.  These 
new  fruits,  which  have  been  named  citranges,  make  a  delightful 
citrangeade  and  may  be  used  in  making  pies,  cakes,  marmalades, 
and  the  like.  In  a  similar  way  Dr.  Webber  has  produced  new 
varieties  of  tangerines,  pineapples,  cotton  ^  plants,  and  grass  for  hay. 

The  work  of  Luther  Burbank1  in  California  has  likewise  resulted 
in  astonishing  colors  and  sizes  of  pinks  and  poppy  blossoms,  in 
plums  and  peaches  of  great  size,  and  in  entirely  new  plants  like  the 
"pomato,"  produced  by  crossing  the  potato  with  the  tomato. 

132.    Some  of   the  valuable  crops  of  New  York  State.2  — 

New  York  ranks  first  of  all  the  States  of  the  Union  in  the 
production  of  the  following  crops : 


NAME  OF  CROP 

ANNUAL  VALUE 
OF  N.  Y.  CROP 

FRACTIONAL 
PART  OF 
U.  S.  CROP 

Hay 

$69,027,200 

1 

Potatoes                        .        .... 

20,996,900 

| 

Other  Vegetables 

25,756,430 

1 

1  See  "New  Creations  in  Plant  Life,"  by  W.  S.  Harwood. 

2  The  authors  are  indebted  to  Professors  of  Cornell  University, 
for  the  use  of  the  figures  recently  compiled. 


PLANT  PROPAGATION 


123 


(Since  dairy  products  are  directly  dependent  on  agricultural 
conditions,  they  are  also  included  in  this  tabulation.) 


Dairy  Products  

$55  474  155 

i 

Milk     

36  284  833 

¥ 
1 

5 

In  spite,  however,  of  its  preeminence  among  the  States  in  the 
production  of  the  crops  just  named,  experts  tell  us  that  the  average 
yield  per.  acre  throughout  the  State  is  probably  less  than  half  what 


FIG.  58.  —  Map  of  New  York  State,  showing  the  crops  grown  in  various 
areas.  —  (Courtesy  of  Prof.  E.  O.  Fippin,  of  Cornell  University.) 

it  should  be  or  might  be  if  more  intelligence  were  used  by  the  aver- 
age farmer.  The  following  quotation  from  an  investigation  made 
among  1303  of  the  farmers  in  the  vicinity  of  Cornell  University, 
near  the  center  of  the  State  of  New  York,  shows  in  a  striking  way 


124  PLANT  BIOLOGY 

the  commercial  advantage  of  even  a  high  school  education.  "Of 
the  owners,  those  who  went  only  to  district  school  made  an  average 
labor  income  of  $318.  The  average  labor  income  of  high  school 
men  was  $622.  Of  the  more  than  high  school  men  (i.e.  college, 
normal,  or  agriculture  courses)  it  was  $847.  The  differences  are 
emphatic.  The  labor  income  of  the  high  school  farmers  is  $304 
greater  than  that  of  the  district  school  men.  This  would  be  5  per 
cent  interest  on  $6080.  In  other  words  the  high  school  education 
of  a  farmer  is  equivalent,  on  the  average,  to  $6000  worth  of  5  per 
cent  bonds."  l 

133.    Summary   of   some   of   the   methods   employed   for 
increasing   crop   production.  —  The   farmers  of  the   future, 


FIG.  59. —  A,  pile  of  corn  resulting  from  cross-pollination  ;  B,  pile  of  corn 
resulting  from  self-pollination.  —  (Bailey.) 

therefore,  to  be  successful  must  have  special  training.  They 
must  be  able  to  carry  on  selection  and  breeding  experiments, 
or  at  least  know  how  to  take  advantage  of  these  experiments 
jn  the  choice  of  their  seeds ;  they  should  know  the  princi- 
ples involved  in  thorough  cultivation  and  in  the  application 
of  manures  and  fertilizers ;  they  should  determine  by  experi- 
ment the  type  of  crop  best  adapted  to  the  soil  of  their  farms, 
and  should  by  proper  rotation  of  crops  (that  is,  by  sowing 
clover  or  other  nitrogen-fixing  plants,  150,  one  year  and  corn 
the  next)  increase  the  fertility  of  their  soil.  If  a  farmer  is  a 
fruit  grower,  he  should  know  how  to  prune  properly,  and  he 

1  An  Agricultural  Survey  of  the  Townships  of  Ithaca,  Dryden, 
Danby,  and  Lansing,  published  by  Cornell  University,  1911. 


PLANT  PROPAGATION  125 

should  practice  grafting  to  develop  better  types  of  fruits.  If 
he  has  soil  adapted  for  woodland,  he  should  plant  forest 
trees,  and  put  into  effect  the  principles  of  forestry.  In  fact, 
there  are  countless  ways  in  which  the  farmer  of  the  future 
can  increase  the  yield  of  his  acres  if  he  but  mixes  brains  with 
the  labor  of  his 


CHAPTER  IX 

PLANTS   IN   THEIR   RELATION   TO   HUMAN   WELFARE 

134.    Introduction.  —  Thus  far  in  our  study  of  plant  biology 
we  have  considered  the  principal   functions  carried  on  by 


FIG.  60.  —  Sweet  potato  plant. 

plants  and  have  observed  some  of  the  adaptations  of  struc- 
ture for  performing  these  functions.  We  have  proved,  for 
example,  that  plants  must  feed,  digest,  breathe,  and  carry 

126 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    127 


on  oxidation  in  order  to  live  and  grow,  and  must  reproduce 
their  kind  in  order  to  perpetuate  the  species.  We  turn  now 
to  a  discussion  of  some  of  the  uses  of  plants  to  man,  and  some 
of  the  ways  in  which  they  are  injurious. 

I.   SOME  OF  THE  USES  OF  PLANT'S  TO  MAN 

135.  Uses  of  plants  for  food.  —  By  repeated  experiments 
we  have  proved  that  various  parts  of  plants  contain  generous 
stores  of  starch, 
sugar,  protein, 
and  mineral  mat- 
ters. In  our  study 
of  human  biology 
we  shall  find  that 
the  foods  which 
are  essential  for 
our  bodies  are 
composed  of  these 
same  substances. 
It  is  for  this 
reason  that  man 
and  other  animals 
are  so  largely 
dependent  upon 
plants  for  food. 
As  examples  we 
may  mention 
roots  like  pars- 
nips,  beets, 
and  sweet  pota- 
toes; stems,  like 
common  potatoes,  asparagus,  and  sugar  cane ;  leaves,  such 
as  cabbage  and  lettuce ;  flowers,  for  example,  cauliflower ; 


FIG.  61.  —  Coffee  tree.  Notice  coffee  berries  along 
sides  of  branches.  —  (Courtesy  of  New  York 
Botanical  Garden.) 


128 


PLANT  BIOLOGY 


fruits,  like  apples  and  peaches;  and  seeds  and  grains,  like 
beans,  wheat,  and  corn. 

136.   Suggestions  for  further   study  of  plants  used  as  food. — 

Study  No.  58.-  (Optional.)  Visit  a  vegetable  market,  make  a  list 
of  the  various  plant  products  sold  for  food,  and  arrange  them  in 
a  table  as  follows : 


NAME  OF  FOOD 

PART  OF  PLANT  EATEN 

Root 

Stem 

Leaf 

Flower 

Fruit 

Seed 

String  beans 

X 

X 

Select  one  or  more  of  the  following  topics  for  special  study:  wheat, 
corn,  potatoes,  oats,  rice.  Consult  Bailey's  "  Cyclopedia  of  Ameri- 
can Agriculture,"  Vol.  II, "  Crops,"  any  encyclopedia,  or  the  publi- 
cations of  the  U.S. 
Department  of 
Agriculture.  De- 
termine (1)  the  parts 
of  the  United  States 
(or  of  the  world) 
in  which  the  crop 
is  raised  in  large 
quantity,  (2)  the 
amount  and  value 
of  a  year's  crop,  (3) 
methods  of  harvest- 
ing and  preparing 
the  crop  for  the 
FIG.  62.  —  Tea  plant.  —  (Bailey.)  market. 

137.  Uses  of  plants  for  flavoring  extracts,  beverages,  and 
medicines.  —  We  saw  in  a  previous  section  that  many  parts 
of  plants  are  available  for  use  as  food  by  man.  Because, 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    129 


also,  of  the  presence  of  various  flavoring  compounds  in  plants, 
the  following  products  are  valuable.  For  instance,  vanilla 
extract  is  made  from  the  vanilla  bean,  pepper  from  pepper 
berries,  horse-radish  from  the  root  of  the  horse-radish  plant, 
and  ginger  from  an  underground  stem. 

We  are  dependent,  too,  upon  plants  for  many  beverages. 
The  coffee  berry  supplies  us  with  coffee,  tea  leaves  with  tea, 
and  from  the  pods 
and  seeds  of  the  cocoa 
tree  we  obtain  cocoa 
and  chocolate. 
Grapes  are  used  to 
make  wines,  from 
apples  cider  is  pre- 
pared, and  from 
grains  of  various 
kinds  other  alcoholic 
liquors  are  produced. 

Quinine,  the  well- 
known  remedy  for 
malaria,  was  formerly 
obtained  from  the 
bark  of  a  tree  known 
as  cinchona,  which 
grows  in  Peru.  This 
medicine  is  now  ob- 
tained almost  exclu- 
sively from  trees  cul- 
tivated in  India  and  other  Eastern  countries.  The  camphor 
tree  furnishes  camphor  gum ;  from  the  juice  of  poppy  fruits 
opium  and  morphine  are  obtained ;  whole  plants  like  pep- 
permint supply  us  with  valuable  medicines.  In  fact,  enormous 
numbers  of  drugs  are  prepared  from  various  parts  of  plants. 


FIG.  63.  —  Chocolate  tree.  —  (Courtesy  of  New 
York  Botanical  Garden.) 


130 


PLANT  BIOLOGY 


138.  Suggestions  for  further  study  of  parts  of  plants  used  as 
drugs.  — Study  No.  59.  (Optional.) 

Visit  a  drug  store  or  consult  an  encyclopedia,  e.g.  Bailey's  "  Cyclo- 
pedia of  American  Agriculture,"  Vol.  II,  "  Crops/'  and  make  a  list 
of  common  drugs  obtained  from  plants.  Fill  out  in  your  note-book 
a  table  like  the  following: 


NAME  OF  DRUG 

PART  OP  PLANT  FROM  WHICH  IT  is  OBTAINED 

Root 

Stem 

Leaf 

Flower 

Fruit 

Seed 

Catnip      .     . 

X 

X 

139.  Uses  of  plants  for  clothing.  —  (Quoted  from  Bailey's 
"  Cyclopedia  of  American  Agriculture,"  Vol.  II,  "  Crops.") 
"  Fiber-producing  plants  are  second  only  to  food  plants  in 
agricultural  importance.  In  continental  United  States, 
however,  cotton,  hemp,  and  flax  are  the  only  fiber  plants 
cultivated  commercially;  and  aside  from  cotton  and  hemp, 
most  of  the  raw  fibers  used  in  our  industries  are  imported." 

"  The  cotton  of  commerce  is  the  hair  or  fiber  on  seeds  of  plants 
belonging  to  the  Mallow  family.  .  .  .  The  plants  are  mostly 
shrubby,  more  or  less  branching,  and  two  to  ten  feet  high.  .  .  . 
The  fruit  consists  of  three-  to  five-celled  '  bolls,'  which  open  at 
maturity  through  the  middle  of  the  cells,  each  cell  liberating  seven 
to  ten  seeds  covered  with  long  fibers.  The  fiber  is  a  tubular  hair- 
like  cell,  T^  to  Yfas  of  an  inch  in  diameter,  somewhat  flattened 
and  spirally  twisted.  It  is  this  latter  characteristic  which  gives 
the  cotton  its  spinning  qualities.  .  .  . 

"  Picking  or  gathering  cotton  in  the  fields  is  a  heavy  item  of 
expense.  It  must  be  picked  by  hand,  as  no  mechanical  appliance  for 
harvesting  has  yet  been  invented  which  gives  satisfactory  results 
in  practical  working.  The  amount  of  cotton  that  one  person  can 
pick  in  one  day  varies  from  one  hundred  to  five  hundred  pounds, 


PLANTS  IN  THEIE  RELATION  TO  HUMAN  WELFARE    131 


FIG.  64.  —  Cotton  picking. 

depending  on  the  skill  of  the  picker.  One  man  can  very  easily 
care  for  the  cultivation  of  twenty  acres  of  cotton,  but  it  requires 
two  to  four  pickers  to  harvest  such  a  crop  rapidly  enough  to  pre- 


132  PLANT  BIOLOGY 

vent  loss.  This  extra  labor  in  harvest  time  is  usually  supplied  by 
the  wives  and  children  of  the  laborers.  The  harvest  season  extends 
over  a  period  of  about  four  months,  beginning  August  15  to  Sep- 
tember 10,  according  to  locality. 

"  Cotton  is  probably  a  native  of  the  tropical  and  semi-tropical 
regions  of  both  hemispheres.  The  earliest  records  of  the  Asiatics 
and  Egyptians  speak  of  it ;  Columbus  found  it  growing  abundantly 
in  the  West  Indies,  while  other  early  explorers  found  it  growing 
in  Mexico  and  South  America.  .  .  .  There  is  no  region  in  the  world 
which  has  such  a  favorable  combination  of  suitable  land,  intelli- 
gent and  plentiful  labor,  cheap  capital  and  adequate  transportation 
facilities  for  the  cultivation  of  cotton  as  the  cotton  belt  of  the 
United  States.  It  has  been  the  chief  source  of  supply  of  the  cotton 
mills  of  the  world,  for  in  this  section  has  been  raised  several  times 
the  quantity  of  cotton  produced  in  all  other  countries  of  the  globe. 
There  are  various  other  countries  which  seem  to  possess  the  soil 
and  climatic  requirements  for  its  growth,  but  for  various  economic 
reasons  the  industry  has  not  been  greatly  developed  in  them; 
however,  a  considerable  quantity  is  produced  in  the  following  coun- 
tries in  the  order  named:  India,  Egypt,  China,  Italy,  Turkey, 
Brazil,  West  Indies,  Mexico,  South  America,  Australia,  and  the 
South  Sea  Islands." 

140.  Further  study  of   fiber-producing  plants.  —  Study  No.    60. 
(Optional.)     Select  one  or  more  of  the  following  fiber-producing 
plants  for  further  study :  flax,  hemp,  jute,  raffia,  hat-straw.     Consult 
Bailey's  "  Cyclopedia  of  American  Agriculture,"  Vol.  II,  "  Crops," 
or  any  encyclopedia.     Determine  (1)  the  parts  of  the  United  States 
(or  of  the  world)  in  which  the  crop  is  raised  in  large  quantity,  (2) 
the  amount  and  value  of  a  year's  crop,  (3)  methods  of  harvesting 
and  preparing  the  crop  for  market. 

II.    THE  USES  OF  FORESTS  AND  FOREST  CONSERVATION 

141.  Uses  of  forests  for  fuel,  lumber,  and  other  commercial 
purposes.  —  In  the  earlier  days  of  our  country's  history  all 
the  fuel  for  heating,  for  running  locomotives  and  other  en- 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    133 

gines  was  supplied  from  the  forests.  About  one  hundred  and 
fifty  years  ago,  coal  was  discovered  in  Pennsylvania,  and  one 
would  suppose  that  since  that  time  our  forests  would  have 
been  drawn  upon  less  heavily  for  fuel.  But  it  is  estimated 
that  the  United  States  burns  annually  at  the  present  time 
one  hundred  million  cords  of  wood.  While  we  are  consider- 
ing the  uses  of  plants  as  fuel,  we  should  remember  that  our 


FIG.  65. — A  view  showing  how  the  forests  of  the  Coal  Period  probably 
looked.  —  (Tarr  and  McMurry.) 

enormous  coal  beds  were  without  doubt  formed  from  great 
tree  ferns  and  other  plants  which  lived  in  bygone  ages.  Pe- 
troleum, too,  from  which  our  kerosene  oil  is  produced,  is 
believed  to  be  a  product  of  plant  decomposition. 

One  has  but  to  call  to  mind  the  enormous  use  of  trees  for 
framing  and  finishing  houses,  for  furniture,  for  railroad  ties, 
telephone  and  telegraph  poles,  for  shipbuilding,  and  for 
boxes,  barrels,  and  paper  manufacture,  to  realize  how  seem- 


\ 
134  PLANT  BIOLOGY 

ingly  indispensable  are  forests.  When  the  early  settlers 
reached  this  country,  they  found  a  virgin  forest  covering  the 
whole  land.  Their  first  work  was  to  clear  1  and  in  order  to  get 
open  spaces  for  cultivation  and  as  a  means  of  protection 
from  attacks  of  the  Indians.  They  cut  down  the  trees  ruth- 
lessly and  the  timber  and  wood  which  was  not  needed  was  left 
to  decay  or  become  the  prey  of  forest  fires.  This  forest  de- 


FIG.  66.  —  Rock  containing  a  fossil  fern  which  grew  in  the  swamps  of  the 
Coal  Period.  —  (Tarr  and  McMurry.) 

struction  has  continued  even  to  our  own  day.  But  at  last 
men  are  beginning  to  see  that  unless  this  slaughter  of  our 
trees  is  stopped,  our  timber  supply  will  soon  be  gone.  In  fact, 
government  experts  tell  us  that  if  the  tree  areas  that  yet  re- 
main are  not  managed  according  to  a  different  system,  twenty 
years  hence  we  shall  reach  the  end  of  the  timber  supply  in  the 
United  States. 

142.   Further  study  of  forest  products.  —  Study  No.  61.     (Op- 
tional.)    Select  one  or  more  of  the  following  forest  products  for  fur- 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE     135 


FIG.  67.  — Wrong  methods  of  lumbering.  —  (Warren.) 


FIG.  68.  —  Right  method  of  lumbering.     Notice  carefully  piled  logs,  wood 
and  brush,  and  uninjured  young  trees. 


136  PLANT  BIOLOGY 

ther  study :  maple  sugar,  rubber,  tar,  turpentine,  wood  pulp,  alcohol, 
charcoal.  Consult  Bailey's  "  Cyclopedia  of  American  Agriculture," 
Vol.  II,  "  Crops,"  or  any  encyclopedia.  Determine  (1)  the  parts 
of  the  United  States  (or  of  the  world)  in  which  the  product  is 
obtained  in  large  quantity,  (2)  the  amount  and  value  of  a  year's 
crop,  (3)  methods  of  preparing  the  product  for  market. 

143.  Uses  of  forests  in  regulating  rainfall  and  flow  of 
streams;  —  We  turn  now  from  a  consideration  of  our  forests 
as  a  source  of  lumber  and  manufactured  products  to  a  dis- 
cussion of  their  effect  on  the  fall  of  rain  and  the  flow  of 
streams.  It  is  probably  true,  in  the  first  place,  that  the 
destruction  of  large  tracts  of  forest  lands  means  a  lessened 
rainfall,  at  least  so  far  as  local  showers  are  concerned.  We 
saw  in  our  study  of  the  functions  of  the  nutritive  organs  of  a 
plant  that  great  quantities  of  water  are  absorbed  by  the  roots, 
carried  up  through  the  woody  bundles  of  the  stem,  and  given 
off  through  the  stomata  of  leaves.  It  has  been  estimated 
that  a  single  oak  tree  of  average  size  gives  off  in  a  single 
season  over  one  hundred  and  twenty-five  tons  of  water.  If 
we  were  to  multiply  this  amount  by  the  number  of  trrees  in  a 
forest,  we  would  get  some  idea  of  the  enormous  amount  of 
water  lifted  into  the  air  by  this  agency. 

Not  only  do  trees  help  to  produce  rain ;  they  also  conserve 
the  rain  when  it  falls  by  holding  it  in  the  soil,  and  preventing 
disastrous  floods.  Let  us  see  how  this  is  brought  about. 
When  the  raindrops  fall  upon  the  tree  tops,  the  water  drips 
from  leaf  to  leaf,  and  finally  reaches  the  ground.  Here  it 
trickles  down  through  the  floor  of  the  forest,  which  is  formed 
of  thick  layers  of  decaying  leaves,  interlacing  roots,  and  earth 
particles  (see  frontispiece).  All  these  form  a  porous  sponge 
which  absorbs  and  holds  back  the  water.  Suppose,  now,  the 
trees  are  removed  from  the  hillsides.  When  the  rains  come, 
there  is  no  means  of  absorbing  the  water ;  instead,  it  flows 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    137 


rapidly  over  the  surface,  swelling  the  streams  into  torrents, 
which  bring  destruction  and  death  as  they  flood  the  valleys 
and  fields  along  their  course.  As  the  water  flows  over  the 
surface  of  the  land  from  which  the  trees  have  been  cut,  it 
carries  along  the  richest  part  of  the  soil,'  thus  causing  loss  of 
fertility  in  the  uplands.  The  material  thus  carried  away 
fills  up  the  river  beds  and  harbor  mouths,  and  in  many  cases 
a  heavy  expense  is  entailed  in  its  removal. 

144.  Dangers  to  forests.  —  We  have  already  called  atten- 
tion to  the  threatened  destruction  of  our  American  forests 
by  careless  lum- 
bering. (See  141.) 
This  means  not 
only  the  whole- 
sale cutting  of 
large  areas  of 
trees,  but  the  lack 
of  forethought 
which  lumber- 
men show  in 

leaving  dead  tree      FIG.  69.  —  Excessive  erosion  of  land  caused   by  de- 
struction of  forests.  —  (Bailey.) 

trunks     and 

branches  to  become  the  prey  of  destructive  forest  fires, 
which,  when  once  started,  devastate  wide  areas.  The  annual 
loss  of  property  from  this  cause  is  conservatively  estimated 
at  more  than  one  hundred  million  dollars. 

This  forest  debris  of  dead  tree  trunks  and  branches  also 
furnishes  breeding  places  for  insects,  which,  when  hatched, 
prey  upon  healthy  trees.  Another  source  of  danger,  espe- 
cially to  young  forest  growth,  comes  from  permitting  large 
flocks  of  grazing  animals  like  cattle  and  sheep  to  feed  upon 
and  trample  down  the  small  trees.  If  we  are  to  preserve  the  • 


138 


PLANT  BIOLOGY 


remnants  of  our  once  vast  forest  resources,  a  public  sentiment 
must  be  thoroughly  aroused  which  will  compel  the  passage 
and  enforcement  of  conservation  laws. 

145.    Necessity  for  reforesting  and  for  forest  protection.  — 
Surely,  enough  has  been  said  to  show  the  necessity  for  forest 

protection.  For- 
tunately, laws 
are  now  being 
passed  that  will 
enable  the  Na- 
tional and  some 
of  the  State  gov- 
ernments to  ac- 
quire large  tracts 
of  land  for  forest 
reservations.  In 
many  States 
these  forest  areas 
will  protect  the 
sources  of  large 
streams.  There 
is  great  need  of 
trained  experts 
who  will  go 
through  the  for- 
ests, mark  the 
trees  which  are 
mature  enough 

to  be  cut,  and  decide  which  way  they  should  fall  to  do 
the  least  damage  to  the  younger  growth.  Again,  large  areas 
now  devastated  should  be  replanted  with  young  forest  trees, 
and  this  is  also  being  done  to  a  considerable  extent.  In  many 


FIG.  70.  —  Planting  young  trees  on  hillsides. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    139 

foreign  countries,  notably  in  Germany,  the  forests  are  so 
used  that  year  after  year  they  supply  the  requisite  timber, 
and  still  continue  to  do  their  much  needed  work  in  conserv- 
ing the  rainfall.  Such  must  be  the  policy  in  our  country 
if  we  wish  to  escape  most  disastrous  penalties  that  always 
result  from  forest  destruction. 

Another  method  of  forest  protection  is  that  afforded  by 
cutting  trees  in  such  a  way  as  to  form  long,  treeless  strips  of 
land  known  as  fire  lanes.  Systems  of  telegraphic  communi- 
cation from  one  part  of  the  forest  reserves  to  another  and  fire 
wardens  are  necessary  factors  in  efficient  protection  of  forests. 

III.     FUNGI    AND    THEIR    RELATION    TO    HUMAN    WELFARE 

146.  Fungi.  —  Thus  far  we  have  confined  our  attention  to 
plants  which  are  easily  visible  to  the  naked  eye  and  which 
consist  of  roots,  stems,  and  leaves.  While  we  ordinarily 
think  of  these  as  the  common  plants,  in  reality  the  most 
common  plant  organisms  are  those  which  have  neither  roots, 
stems,  nor  leaves,  and  which  in  many  cases  are  microscopic 
in  size.  The  smallest  and  most  numerous  of  these  are  known 
as  bacteria,  which  are  found  all  about  us,  in  the  soil,  in  the  air 
we  breathe,  on  the  food  we  eat,  and  in  the  water  we  drink. 
Bacteria  belong  to  a  great  group  of  plants  called  fungi. 
All  fungi  are  characterized  by  the  absence  of  chlorophyll, 
hence  plants'  of  this  group  cannot  manufacture  their  carbo- 
hydrate food  out  of  materials  from  the  soil  and  air,  -but  are 
dependent  on  foods  made  by  green  plants.  More  familiar 
to  us,  perhaps,  than  bacteria  are  the  fungi  known  as  mush- 
rooms and  toadstools,  and  the  molds  and  mildews.  Still 
other  fungi  are  the  yeasts,  the  rusts,  and  the  smuts.  Because 
of  the  enormous  economic  importance  of  many  of  these  forms, 
we  shall  consider  more  or  less  in  detail  the  structure,  func- 
tions, and  life-history  of  several  of  them, 


140  PLANT  BIOLOGY 


A.   Bacteria1 

147.  Microscopical  appearance  and  size  of  bacteria.  — 
Every  one  is  familiar  with  the  fact  that  if  a  bouquet  of  flowers 
is  left  for  some  time  in  a  vase  of  water,  the  stems  decay  and 
disagreeable  odors  are  given  off.  This  is  a  common  example 
of  the  action  of  bacteria,  for  all  decay  is  due  to  the  work  of 
these  organisms.  When  we  come  to  examine  the  flower-stems 
or  the  putrid  water,  we  find  a  slimy  scum.  If  we  put  a  drop 
of  this  scum  on  a  slide,  cover  with  a  cover-glass,  and  examine 
with  the  highest  powers  of  the  microscope,  usually  we  would 
see  many  different  forms  of  living  things.  Some  of  them 
would  probably  appear  relatively  large,  and  these,  as  we  shall 
see  later  (Chapter  IV,  "  Animal  Biology  ")  /are  single-celled  ani- 
mals. A  closer  examination  will  disclose  countless  numbers 
of  very  minute,  colorless  organisms ;  these  are  the  bacteria. 
A  careful  study  of  many  kinds  of  bacteria  shows  that  they  have 
several  characteristic  shapes  (see  Fig.  71)  by  means  of  which 
they  can  be  roughly  classified.  Some  are  rod-shaped  (like  a 
firecracker) ,  some  are  spherical,  or  egg-shaped,  and  still  others 
are  spiral-shaped.  Each  bacterium  is  a  tiny  bit  of  translucent 
protoplasm,  inclosed  in  a  cell  wall  of  cellulose.  Thus  far  no 
nucleus  has  been  discovered  in  any  kind  of  bacteria.  Be- 
cause of  their  cellulose  walls,  and  because  of  their  likeness 
to  certain  low  forms  of  green  plants,  biologists  now  regard 
these  organisms  as  plants  rather  than  animals. 

Some  of  the  rod-shaped  bacteria  have  one  or  more  long, 
hairlike  projections  from  the  ends,  called  cil'i-a,  which  give 
the  germs  still  further  resemblance  to  firecrackers.  These 
cilia  lash  about  rapidly,  and  thus  drive  the  cells  through  the 

1  Because  of  the  importance  of  bacteria  in  relation  to  sanitation, 
it  may  be  found  advisable  to  consider  this  whole  topic  in  connection 
with  human  biology.  Sections  148-164  will  therefore  be  repeated 
in  the  book  on  human  biology. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    141 


water.  The  spiral  bacteria  roll 
over  and  over,  and  advance  in  a 
spiral  path  like  a  corkscrew.  Other 
forms  have  rapid  movements,  but 
it  is  not  known  how  they  are  ac- 
complished. 

It  is  very  difficult  to  get  any 
clear  notion  of  the  extreme  minute- 
ness of  bacteria.  It  means  but 
little  to  say  that  the  rod-shaped 
forms  are  -^nr  of  an  inch  in  length. 
The  imagination  may  be  somewhat 
assisted  if  we  remember  that  fifteen 
hundred  of  them  arranged  in  a 
procession  end  to  end  would 
scarcely  equal  the  diameter  of  a 
pin  head. 

148.  Reproduction  of  bacteria. 
—  When  conditions  are  favorable, 
the  production  of  new  cells  goes 
on  with  marvelous  rapidity.  The 
process  is  something  as  follows : 
The  tiny  cells  take  in  through  the 
cell  wall  some  of  the  food  materials 
that  are  about  them,  change  this 
food  into  protoplasm,  and  thus 
increase  somewhat  in  size.  The 
limit  is  soon  reached,  however,  and 
the  bacterium  begins  to  divide 
crosswise  into  halves.  The  mother 
cell  thus  forms  two  daughter  cells 
by  making  a  cross  partition  (cell  wall  of  cellulose)  between  the 
two  parts.  (See  Fig.  71,  C.)  If  the  daughter  cells  cling  to- 


FIG.   71.  —  Various    forms 
bacteria. 

A,  a  colony  of  spherical  bac- 
teria (coccus,  plur.  cocci) ; 
B,  rod-shaped  bacteria  (ba- 
cillus, plur.  bacilli)  ;  C,  rod- 
shaped  bacteria  dividing ; 
D,  rod-shaped  bacteria,  each 
containing  a  spore  ;  E,  spiral 
bacteria  (spirillum,  plur. 
spirilla)  each  with  cilia. 


142  PLANT  BIOLOGY 

gether,  a  chain  or  a  mass  is  formed.  Oftentimes  they  separate 
entirely  from  each  other.  In  either  case  the  whole  mass  of 
bacteria  is  called  a  colony. 

It  usually  takes  about  an  hour  for  the  division  to  take  place. 
Suppose,  then,  we  start  at  ten  o'clock  some  morning  with  a 
single  healthy  bacterium.  If  conditions  are  favorable,  there 
would  be  two  cells  at  eleven  o'clock,  and  by  twelve  o'clock 
each  of  these  two  daughter  cells  would  form  two  granddaugh- 
ter cells;  the  colony  would  then  number  four  individuals. 
Should  this  process  continue  for  twenty-four  hours,  or  until 
ten  o'clock  on  the  day  after  the  single  bacterium  began  its 
race,  the  colony  would  number  16,777,216  bacteria.  "  It 
has  been  calculated  by  an  eminent  biologist,"  says  Dr. 
Prudden.,1  "  that  if  the  proper  conditions  could  be  maintained, 
a  rodlike  bacterium,  which  would  measure  about  a  thou- 
sandth of  an  inch  in  length,  multiplying  in  this  way,  would  in 
less  than  five  days  make  a  mass  which  would  completely  fill 
as  much  space  as  is  occupied  by  all  the  oceans  on  the  earth's 
surface,  supposing  them  to  have  an  average  depth  of  one  mile." 

149.  Necessary  conditions  for  the  growth  of  bacteria.  — • 
Such  startling  possibilities  as  those  suggested  in  the  preceding 
section  fortunately  can  never  become  realities,  for  the 
favorable  conditions  to  which  we  have  referred  soon  cease  to 
exist.  Bacteria,  like  all  other  living  organisms,  require  food, 
oxygen,  moisture,  and  a  certain  degree  of  warmth.  Let  any 
one  of  these  conditions  be  withheld,  and  the  cells  either  die 
or  cease  to  be  active.  Sometimes,  when  food  or  moisture 
begins  to  fail,  the  protoplasm  within  each  cell  rolls  itself 
into  a  ball  and  covers  itself  with  a  much  thickened  wall. 
This  protects  it  until  it  again  meets  with  conditions  favorable 
for  growth.  The  process  we  have  been  describing  is  known  as 

1  "  The  Story  of  the  Bacteria,"  by  Dr.  T.  Mitchell  Prudden.  G.  P. 
Putnam's  Sons,  New  York. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    143 

spore  formation;  the  tiny  protoplasmic  sphere  is  called  a  spore, 

and  its  dense  covering  a  spore  wall.     (Fig.  71,  D.)     In  this 

condition     bacteria    may    be    blown 

hither  and  yon  as  a  part  of  the  dust. 

They  may  be  heated  even  above  the 

temperature  of  boiling  water  without 

being    killed.     Whe,n  at   length   they 

settle  down  on  a  moist  surface  that 

will  supply  them  with  food,  the  spores 

burst    their    thick    envelope,    assume 

once  more  their  rod-shaped  or  spiral 

form,  and  go  on  feeding,  assimilating, 

and  reproducing  their  kind. 


150.  Relation  of  bacteria  to  soil 
fertility. — Having  discussed  somewhat 
the  structure  and  functions  of  bacteria, 
we  are  now  to  consider  the  great  im- 
portance of  these  microscopic  organ- 
isms to  human  welfare.  In  the  first 
place,  were  it  not  for  their  never  end- 
ing activity,  all  life  upon  the  earth 
would  soon  cease  to  exist.  Let  us  see 
why  this  is  so.  When  animals  or  plants 
die,  their  bodies  fall  upon  the  ground, 
and  were  these  lifeless  masses  not  taken  _ 

FIG.  72.  — Roots   of   horse 

care  of,  the  whole  surface  of  the  earth    bean,  showing  numerous 
would  long  since  have  been  covered    root-tubercles.  —  (Stras- 

. , ,  burger.) 

with  a  vast  number  of  unbuned  or- 
ganisms.    All  this  dead  material,  however,  as  we  have  seen, 
is  food  for  the  countless  bacteria;  they  cause  it  to  decay, 
and  thus  decompose  it  into   simpler   chemical  compounds 
that  can  soak  into  the  earth  and  then  be  used  in  the  nu- 


144  PLANT  BIOLOGY 

trition  of  the  higher  plants.  And  since  plants  are  con- 
stantly taking  from  the  soil  the  food  materials  which  they 
need,  this  soil  would  tend  to  become  less  and  less  fertile 
were  it  not  for  the  work  of  the  bacteria  that  caused  de- 
composition. This  is  the  reason  why  rotting  manure  adds 
to  the  fertility  of  soil. 

Again  it  has  been  proved  that  certain  kinds  of  bacteria 
directly  increase  the  amount  of  nitrogen  compounds  that  are 

so    essential     for    plant 

K*  o^     Ck      A     growth.       It    has     long 

c^^  eH5       Is      been   known   that    corn 

L     ^^^^      -          &s*         and  other  crops  will  grow 

better  in  soil  that  has 
just  borne  a  crop  of  peas, 
beans,  clover,  or  other 
members  of  the  pea 
family.  Within  recent 
years  an  explanation  of 
this  fact  has  been  found. 
When  the  roots  of  those 
,-,  ~Q  „  .  ,  pod-bearing  plants  are 

FIG.  73.  —  Bacteria  from  root-tubercles. —    " 

(Duggar.)  examined,  small  swellings 

are  seen.     These  contain 

multitudes  of  bacteria  that  are  able  to  take  the  free  nitrogen 
from  the  air,  where  it  exists  in  such  abundance,  and  store  it 
away  in  the  form  of  nitrates  which  are  very  important  mineral 
matters  needed  by  all  crops.  Since  those  bacteria  can  be  put 
into  soils  that  do  not  have  them,  it  may  be  possible  in  the 
near  future  to  restore  much  of  the  fertility  which  has  been  lost. 

151.  Relation  of  bacteria  to  the  flavors  of  food.  —  Again, 
many  of  the  flavors  of  food  are  due  to  the  action  of  bacteria. 
Meats,  for  instance,  when  freshly  killed,  are  tough  and  taste- 
less. If  allowed  to  stand,  however,  by  the  decomposing 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    145 

action  of  bacteria  these  meats  become  tender  and  acquire 
their  distinctive  flavors.  A  similar  action  takes  place  when 
butter  or  cheese  ripens,  and  the  dairy  industry  has  been  per- 
fected to  such  a  degree  that  bacteria  of  certain  kinds  have 
been  proved  to  give  rise  to  definite  flavors,  and  these  bacteria 
can  be  produced  in  pure  cultures  for  the  dairymen. 

152.  Bacteria  in  the   industries.  —  Without  the  help  of 
bacteria  the  preparation  of  linen,  jute,  and  hemp  would  be 
impossible.     All   these   valuable   products   are   plant  fibers 
which  are  connected  with  woody  materials  so  closely  that  they 
cannot  be  separated  without  first  subjecting  the  stems  of 
flax,  hemp,  and  jute  to  a  process  of  decay  in  large  tanks  of 
water.     Moisture  and  warmth  induce  the  rapid  growth  of 
germs,  and  this  process  loosens  the  tough  fibers  so  they  can 
be  separated  from  the  useless  parts  of  the  plant. 

The  change  of  alcohol  into  vinegar  is  caused  by  bacteria. 
Likewise  in  the  preparation  of  indigo  other  forms  of  bacteria 
are  all  important. 

153.  Bacteria  as  the  foes  of  man.  —  Unfortunately,  how- 
ever, there  are  certain  germs  that  find  favorable  conditions 
for  growth  only  in  living  animal  tissue.     Thus  the  bacterium 
of  consumption  grows  in  the  lungs,  the  germ  of  diphtheria  in 
the  throat,  and  the  bacteria  that  cause  typhoid  fever  in  the 
intestines.     These  disease-producing  germs  are  called  by  Dr. 
Prudden  "  man's  invisible  foes."     Yet  wonderful  progress  is 
being  made  in  the  fight  against  them.     We  have  learned  how 
to  check  the  ravages  of  cholera,  typhoid,  and  diphtheria,  and 
even  consumption  is  found  to  be  a  preventable  disease. 
Further  discussion  of  bacteria  will  be  found  in  several  of  the 
subsequent  chapters.1 

1  For  laboratory  work  on  bacteria,  see  Chapter  II,  "Human  Bi- 
ology." Also  consult  Peabody's  "  Laboratory  Exercises  in  Anatomy 
and  Physiology"  (1902),  pp.  100-107. 


146  PLANT  BIOLOGY 

B.    Yeast   (Optional) 

164.  Microscopical  appearance  and  size  of  yeast.  —  A  small 
piece  of  a  cake  of  compressed  yeast,  mixed  in  a  spoonful  of  water, 
forms  a  milky  fluid  that  is  much  like  so-called  bakers'  or  brewers' 
yeast.  If  we  examine  with  the  microscope  a  bit  of  this  mixture 
in  the  same  way  in  whicJji  the  bacteria  were  studied,  we  find  that  it 
consists  of  innumerable  bodies  of  minute  size.  These  are  yeast 
cells.  Each  cell  is  more  or  less  egg-shaped,  and  is  composed  of  color- 
less protoplasm  inclosed  within  a  wall 
of  cellulose.  By  the  use  of  special 
stains,  a  nucleus  becomes  visible. 
(The  spherical  dots  seen  in  fresh  yeast 
cells  are  known  as  vacuoles  and  are 
filled  with  a  colorless  liquid.)  Yeast, 
like  bacteria,  is  regarded  as  one  of  the 
lowest  forms  of  plant  life. 

155.    Reproduction  of  yeast.  —  Most 
of   the   cells   that  we   are   looking  at 
are  not  separate   individuals,  but  are 
FIG.  74.  — Yeast  cells,  showing  strung  together  in  little  chains.     This 
method  of    reproduction  by  ,     ,    ,      ,  f  His/Mission    of   thp 

budding.     Nuclei  are  not  lact 
shown.    Clear  spaces  are  vac-  method  of  reproduction  of  yeast.   When 

uoles-  there   is   a  sufficient   supply   of  food, 

moisture,  and  oxygen,  and  when  the  temperature  is  favorable, 
these  living  plant  cells  begin  to  feed  and  to  grow.  They  soon  reach 
their  full  size,  and  then  the  cell  wall  is  pushed  out  at  the  side  by  the 
growing  protoplasm.  In  this  way  a  bud  is  formed.  This  continues 
to  grow  and  soon  becomes  a  daughter  cell,  closed  off  from  the  mother 
cell  by  a  wall  of  cellulose.  Meanwhile,  one  or  more  buds  may  be 
forming  on  the  outside  of  the  daughter  cells.  If  all  these  cells 
cling  together,  a  colony  is  formed  which  consists  of  a  mother  cell 
(largest  in  size),  one  or  more  daughter  cells,  and  several  tiny  grand- 
daughter cells.  The  individual  cells  are  easily  separated  from  one 
another.  This  method  of  reproduction  is  known  as  budding  (Fig.  74) . 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    147 

166.  Changes  caused  by  yeast.  —  A  yeast  mixture  may  be  easily 
prepared  for  experimentation  by  pouring  into  a  jar  a  cup  of  water, 
adding  a  spoonful  of  molasses,  and  a  spoonful  of  the  milky  fluid 
made  as  described  in  154. 

If  the  jar  with  its  contents  is  set  aside  in  a  warm  place  (70°  to 
90  °  F.)  for  a  short  tune,  it  begins  to  "  work,"  and  bubbles  of 
gas  rise  to  the  surface.  At  the  end  of  several  hours,  we  notice 
that  the  sweetness  of  the  molasses  is  disappearing,  that  the  mixture 
begins  to  smell  sour,  and  that  a  sharp,  biting  taste  is  becoming  evi- 
dent. All  these  changes  are  caused  by  the  growth  of  living  yeast 
cells. 

Xow,  what  is  the  gas  that  is  formed  in  this  process,  and  what 
causes  the  changes  in  taste  and  odor?  To  answer  these  questions 
we  must  carry  our  experiments  still  further.  When  the  mixture 
is  "  working  "  well,  the  bottle  should  be  tightly  closed  with  a  rubber 
stopper,  through  which  extends  one  arm  of  an  inverted  U-shaped 
tube.  The  other  end  of  this  tube  should  run  over  to  the  bottom 
of  a  test  tube  half-filled  with  limewater.  The  gas  that  has  been 
rising  through  the  yeast  mixture  now  passes  through  the  U-tube, 
and  as  it  comes  in  contact  with  the  limewater,  the  latter  changes  to 
a  milky-white  color.  This  proves  that  the  gas  formed  during  the 
growth  of  yeast  is  carbon  dioxid. 

After  "  working  "  a  day  or  two,  the  yeast  mixture  will  have  a 
strong  taste  and  odor.  A  part  of  it  should  then  be  poured  into  a 
glass  Florence  flask  (commonly  used  in  the  chemical  laboratory 
for  boiling  liquids),  and  the  mouth  should  be  closed  by  a  rubber 
stopper.  The  short  arm  of  a  long  delivery  tube  should  be  passed 
through  this  stopper.  When  the  flask  is  heated  gently,  some  of  the 
liquid  is  changed  to  a  vapor.  If  the  delivery  tube  is  cooled  by  cov- 
ering it  with  cloths  wet  in  cold  water,  the  vapor  condenses  into  a 
liquid,  which  comes  from  the  end  of  the  tube  in  drops.  This  opera- 
tion we  have  been  describing  is  known  as  dis-til-la'tion.  In  distilling 
a  liquid,  we  first  convert  it  into  a  vapor,  and  then  condense  this  vapor 
into  a  liquid.  After  collecting  a  few  spoonfuls,  the  liquid  should  be 
slowly  distilled  a  second  time.  Then  we  obtain  a  colorless  fluid 
that  has  the  distinct  smell  and  taste  of  alcohol.  It  burns,  too,  with 


148  PLANT  BIOLOGY 

a  pale  blue  flame.  And  so  we  learn  that  yeast,  as  it  grows  in  the 
molasses  mixture,  changes  the  sweet  substances  into  carbon  dioxid  and 
alcohol,  a  process  that  is  known  as  alcoholic  fer-men-ta'tion. 

157.  Uses  of  yeast.  —  When  bread  is  made,  water  (or  milk), 
butter,  salt,  sugar,  and  yeast  are  added  to  flour.  After  the  mixture 
has  been  stirred  together,  a  sticky  mass  of  dough  is  formed,  which 
in  a  warm  place  begins  to  rise.  This  is  due  to  the  fact  that  the  yeast 
cells  change  the  sugar  into  alcohol  and  carbon  dioxid.  Bubbles  of 
gas  are  thus  imprisoned  in  the  sticky  dough.  While  expanding  and 
seeking  to  escape,  they  make  the  solid  mass  porous.  After  the  bread 
has  risen  sufficiently,  it  is  kneaded  in  order  to  break  up  the  large 
bubbles  and  in  order  to  distribute  the  gas  throughout  the  dough. 
When  the  bread  is  baked,  the  alcohol  and  carbon  dioxid  pass  off 
into  the  air,  leaving  the  bread  light  and  digestible.  These  minute 
organisms  are  also  of  great  commercial  importance  in  the  manufac- 
ture of  alcohol  and  of  all  kinds  of  liquors.  It  is  known  that 
yeast  cells  are  found  commonly  in  the  air.  As  different  kinds  of 
fruits  ripen,  they  are  usually  more  or  less  covered  with  yeast  or 
its  spores.  When,  therefore,  grapes  are  gathered  and  their  juice  is 
pressed  out,  the  sweet  liquid  is  soon  alive  with  the  busy  cells,  and 
fermentation  begins  at  once.  In  this  way  wines  are  produced. 
Cider  is  produced  by  the  fermentation  of  apple  juice. 

In  the  manufacture  of  beer  and  of  other  malt  liquors,  barley  is 
commonly  used.  The  grain  is  soaked  and  allowed  to  sprout  for 
a  short  time,  until  the  starch  is  changed  to  grape  sugar.  The  barley 
kernels  are  then  killed  by  heat  to  prevent  further  changes,  and  the 
grain  is  then  known  as  malt.  When  this  is  put  into  water,  the  sugar 
is  extracted.  Yeast  is  then  added,  and  the  mass  ferments.  The 
beer  thus  formed  contains  2  to  5  per  cent  of  alcohol. 

Distilled  liquors,  or  spirits,  are  obtained  from  wines  and  other 
fermented  liquors  by  the  process  of  distillation,  the  principles  of 
which  have  already  been  explained.  Brandy  is  made  by  distilling 
wine,  whisky  is  obtained  from  fermented  corn  and  rye,  and  rum  is 
manufactured  from  molasses.  All  of  these  liquors  contain  a  large 
percentage  of  alcohol  (40  to  50  per  cent). 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE     149 

158.  Suggestions  for  laboratory  work  on  yeast.  —  No.  62. 
Students  should  examine  the  appearance  of  yeast  cells  under  the 
low  and  high  powers  of  the  compound  microscope.  If  time  permits, 
the  demonstration  of  carbon  dioxid  production  and  of  distillation 
of  alcohol  might  well  be  made.  (See  Peabody's  "  Laboratory  Exer- 
cises/' pp.  94-99,  Henry  Holt  &  Co.,  New  York  City.) 

C.   Bread  Mold  (Optional) 

169.  Structure  of  bread  mold.  —  If  pieces  of  bread  or  cake  be 
moistened,  and  placed  in  a  dish,  and  covered  with  a  bell- jar  in  the 


--c 


FIG.  75.  —  Bread  mold,  showing  nutritive  hyphae  (A)  ;  reproductive  hyphse 
CB) ;  and  spore  cases  (C).  — (Osterhout.) 


dark,  in  a  few  days  grayish  patches  will  appear  in  places  on  the 
surface  of  the  bread.  This  growth  is  due  to  the  activity  of  one 
of  the  fungi,  known  as  a  mold,  and  will  probably  be  the  kind 
called  bread  mold.  No  care  is  required  to  produce  the  plant  in 
quantities;  on  the  contrary,  as  common  experience  shows,  some 
pains  must  be  taken  by  the  housekeeper  to  prevent  it  from  spoil- 
ing food. 

When  the  bread  mold  is  examined  with  a  hand  lens,  it  is  seen  to 


150  PLANT  BIOLOGY 

consist  of  a  mass  of  fine  interlacing  threads  called  the  mycelium. 
(See  Fig.  75.)     Single  threads  are  known  as  hyphce. 

160.  Reproduction  and  life  history  of  bread  mold.  —  Some  of 
the  hyphae  in  their  growth  assume  an  upright  position,  and  each  of 
these  at  the  upper  end  develops  a  little  globular  white  mass  or  spore 
case.    (See  Fig.  75.)    An  examination  with  the  high  power  of  the 
microscope  shows  that  the  spore  cases  are  filled  with  tiny  cells 
known  as  spores.     When  the  spores  are  ripe,  the  spore  cases  appear 
brown  or  black,  they  break  open,  and  the  spores  are  scattered. 
If  these  spores  fall  on  food  of  some  kind,  such  as  bread,  they  begin 
to  germinate,  and  each  one  produces  another  mass  of  threads  with 
spore  cases  on  erect  hyphse.     In  other  words,  the  mold  produces 
spores  and  the  spores  reproduce  the  mold.     The  spores  of  molds 
are  in  the  air  nearly  everywhere,  hence  we  see  why  molds  appear 
so  quickly  on  foods  of  various  kinds,  provided  they  are  moist  and  in 
a  warm  place. 

161.  Nutrition  in  the  fungi.  —  Molds,  like  other   fungi,  as   we 
have  already  said,  cannot  manufacture  their  own  food  out  of  the 
materials  obtained  from  the  soil  and  air,  but  are  dependent  on  foods 
made  by  green  plants.     Certain  of  the  threads  called  the  nutritive 
hyphce  form  ferments  which  digest  the  food  compounds  found  in 
bread  or  other  substances  on  which  the  mold  is  growing,  and  then  the 
digested  food  is  absorbed,  used  in  growth,  and  in  the  production  of 
energy.    Other  threads  develop  the  spore  cases  and  so  are  called  re- 
productive hyphce.    Hence,  it  is  evident  that  fungi,  like  all  plants,  carry 
on  both  nutritive  and  reproductive  functions,  but  on  account  of  the 
lack  of  chlorophyll  are,  like  animals,  dependent  on  the  green  plants 
for  their  supply  of  food. 

162.  Suggestions   for  laboratory  work   on  bread   mold.  —  No. 
63.     Sow  bread   mold  as  suggested  in  159   in   sufficient   quantity 
to  supply  each  two  pupils  with  a  piece  of  the  moldy  bread.     Pupils 
should  examine  a  specimen  with  a  hand   magnifier,  describe    the 
appearance  of    the   mycelium   and   hyphse    bearing    spores,    and 
should  then  make  a  drawing  to  show  these  points.     Some  of  the 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    151 

spore  cases  should  be  placed  on  a  slide  in  water  and  covered  with  a 
cover  glass.  If  the  glass  cover  is  tapped  with  a  pencil,  some  of  the 
spore  cases  will  be  ruptured.  The  preparation  should  then  be  ex- 
amined with  the  high  power  of  the  compound  microscope,  and  the 
ruptured  spore  cases  drawn,  together  with  a  few  of  the  escaping 
spores. 

D.    Other  Fungi  (Optional) 

163.    Mushrooms.  —  Mushrooms  are  forms  of  fungi  which  are 
often  called    "  toadstools,"    especially   if   they  are    supposed   to 


FIG.  76.  —  An  edible  mushroom. 

be  poisonous.  All  fungi  of  this  kind  should,  however,  be  called 
mushrooms,  since  their  structure  and  life  history  are  similar.  The 
conspicuous  part  of  the  plant,  the  umbrella  shaped  structure  so 
familiar  to  all,  is  really  the  reproductive  organ  of  the  plant,  the  part 
that  bears  the  spores  (Fig.  76).  The  nutritive  organs  are  a  mass  of 
threads  (as  in  the  mold)  which  lie  beneath  the  surface,  where  they 
absorb  the  foods  from  some  decaying  material  in  the  soil  to  give 
rise  to  the  reproductive  body. 


152 


PLANT  BIOLOGY 


As  indicated  above,  many  mushrooms  are  poisonous,  but  a  few 
kinds  are  known  to  be  edible.1  Mushrooms  are  not  especially  nu- 
tritious ;  that  is,  they  cannot  take  the  place  of  the  cereals  and  other 
staple  foods,  but  they  serve  to  add  to  the  variety  of  materials  which 
are  more  valuable  for  their  flavoring  qualities  than  for  the  quantity 
of  nutriment  they  contain.  Commercially  the  cultivated  mush- 
room is  of  considerable  importance,  especially  in  Europe.  Paris 
is  said  to  be  the  center  for  the  sale  of  this  product.  In  the  year 

1901  it  was  estimated  that  10,000,000 
pounds  of  cultivated  mushrooms 
passed  through  the  markets  of  Paris. 
In  this  country  the  mushroom  is  of 
commercial  importance  only  in  the 
regions  of  the  larger  cities. 

164.  Rusts  and  smuts.  —  The 
fungi  known  as  rusts  receive  their 
name  from  the  rusty  appearance  in 
an  early  stage  of  their  growth  which 
they  cause  on  the  stems  and  leaves 
of  plants  which  they  attack.  The 
cereals,  wheat,  oats,  barley,  and  rye, 
are  the  crops  which  this  fungus  in- 
jures most.  In  the  case  of  wheat, 
half  of  the  crop  or  even  more  may 
be  destroyed. 

The  very  suggestive  name  of  smut 
is  given  to  another  fungus  which 

affects  all  the  cereals  named  above,  and  corn  as  well.  In  the  case 
of  corn,  this  plant  often  affects  the  ears  as  well.  The  name  is 
probably  given  on  account  of  the  appearance  of  the  mass  of  black 
spores.  If  one  touches  these  spores,  especially  those  of  corn  smut, 
with  the  finger,  and  then  rubs  the  finger  on  some  white  paper  or 

1  So  many  deaths  are  caused  by  using  poisonous  instead  of  edible 
mushrooms  that  it  is  never  safe  to  eat  wild  forms  until  they  have 
been  identified  by  an  expert. 


FIG.  77. —  Corn  smut  on  an  ear 
of  corn. 


PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE    153 

cloth,  a  sooty  mark  is  left.  The  damage  done  by  smuts  is  very 
considerable.  In  case  of  the  corn  crop  alone  it  has  been  estimated 
that  a  yearly  loss  of  20  per  cent  of  the  crop,  or  $20,000,000,  is  caused 
thereby,  and  in  the  other  cereal  crops  the  loss  is  even  greater.  It 
should  be  mentioned  in  closing  this  discussion  tha.t  the  rusts  and 
smuts  are  only  two  of  a  large  number  of  fungous  diseases  that  affect 
plants. 


CHAPTER  X 
PLANT  CLASSIFICATION 

I.   COMMON  METHODS  OF  CLASSIFICATION 

165.  Herbs,  shrubs,  and  trees.  —  One  way  of  classifying 
the  common  plants  with  which  we  are  most  familiar  is  that 
of  calling  them  either  herbs,  shrubs,  or  trees.  This  classifica- 


FIG.  78.  —  Base  of  one  of  the  giant  trees  of  California.  — (Tarr  and  McMurry.) 


tion  is  based  upon  the  general  similarity  in  size,  form,  and 
texture  of  the  plants  which  are  assigned  to  each  group.  Thus 
when  we  think  of  a  tree  we  have  in  mind  a  plant  which,  when 

154 


PLANT  CLASSIFICATION 


155 


156 


PLANT  BIOLOGY 


mature,  is  of  large  size,  with  a  single  woody  trunk  and  branches. 
This  trunk  may  extend  up  nearly  to  the  top  of  the  tree,  as  in 
the  case  of  the  pines  and  spruces,  or  some  distance  above  the 
ground  the  trunk  may  divide  into  branches,  as  is  true  in  the 
elms  and  maples. 

A  shrub,  on  the  other  hand,  is  usually  of  smaller  size  even 
when  fully  grown  than  is  a  tree;  it  commonly  does  not  have  a 
single  trunk,  but  several  woody  stems  which  often  start  from 
the  ground  level,  as  in  the  lilac,  rose, 
and   witch   hazel.      Both    shrubs    and 
trees  are  alike  in  that  their  stems  and 
branches  do  not  die  down  to  the  ground 
at  the  end  of  the  season. 

An  herb,  as  the  term  is  used  in  plant 
biology,  is  a  plant  of  relatively  small 
size,  with  comparatively  little  woody 
material  in  its  stem,  which  dies  down  to 
the  ground  level  at  the  close  of  the 
season.  Such  are  beans,  corn,  and 
morning  glories.  The  roots  or  under- 
ground stems  of  some  herbs  —  for  ex- 
ample, dahlias,  carrots,  and  parsnips  — 

remain  alive  ready  for  growth  the  next  year.  These  facts 
suggest  another  method  of  classifying  plants,  namely,  as  : 

166.  Annuals,  biennials,  and  perennials.  —  When  a  plant 
attains  its  maturity  in  one  season's  growth  and  then  dies,  as 
do  beans,  corn,  and  morning  glories,  such  a  plant  is  called  an 
annual.  Many  plants  which  have  fleshy  roots,  like  the  beet, 
carrot,  and  parsnip,  do  not  produce  flowers  and  seeds  until  the 
second  year.  During  the  first  season  after  the  seed  is  planted 
the  food  manufactured  in  the  leaves  passes  down  the  plant 
and  is  storecj  beneath  the  ground.  At  the  end  of  the  season 


FIG.  80.  —  An  herb. 


PLANT  CLASSIFICATION 


157 


the  stems  and  leaves  above  ground  die ;  but  if  this  root  re- 
mains in  the  ground  or  is  planted  the  next  season,  stems, 
leaves,  and  flowers  develop  rapidly,  and  finally  seeds  are 


FIG.  81.  —  Carrot.    A,  young  seedling;    B,  enlarging  root  early  in  season; 
C,  section  of  enlarged  root  late  in  season. 

formed,  the  food  stored  up  the  preceding  season  being  drawn 
upon  for  the  development  of  these  parts.  Plants  which  have 
a  life  history  like  this  and  which  live  for  two  years  only  are 


158 


PLANT  BIOLOGY 


called  biennials  (Latin,  bi  =  two -\-annus  =  year).  Perennials 
are  plants  that  live  year  after  year.  Hollyhocks  and  dahlias, 
for  instance,  store  food  in  fleshy  roots  year  after  year,  while 
the  parts  above  ground  die,  as  in  the  case  of  beets  and  carrots. 
Other  perennials,  like  trees  and  shrubs,  lose  only  their  leaves 
at  the  end  of  each  season. 

167.  Deciduous  and  evergreen  trees  and  shrubs.  —  Trees 
and  shrubs  may  be  classified  as  evergreen  or  deciduous.     Since 
the  leaves  of  pines,  spruces,  and  hemlocks  remain  green  and 
attached  to  the  stem  during  the  winter,  these  plants  are  known 
as  evergreens.     Certain  shrubs  (rhododendrons,  arbutus,  and 
wintergreen,    for    example)    also    keep    their   green    leaves 
throughout  the  winter,  and  so  in  a  sense  they  may  be  regarded 
as  evergreens.     Maples,  elms,  and  horse-chestnuts,  on  the 
other  hand,  shed  their  leaves  in  autumn ;  they  are  therefore 
said  to  be  deciduous  (Latin,  de  =  from-\-cadere  =  to  fall). 

168.  Field   work    on   plant    classification.      Optional.  —  No.    64. 

If  possible,  teachers  should  accompany  their  pupils  on  a  field  trip, 
point  out  and  name  the  plants  best  adapted  for  a  study  in  classifi- 
cation, using  perhaps  an  outline  like  the  following: 


NAME  OF 
PLANT 

HERB 

SHRUB 

TREE 

SIMPLE 
LEAVES 

COM- 
POUND 
LEAVES 

OPPO- 
SITE 
LEAVES 

ALTER- 
NATE 
LEAVES 

DECID- 
UOUS 

EVER- 
GREEN 

Rose  . 

X 

X 

X 

X 

II.    SCIENTIFIC  METHOD  OF  CLASSIFICATION 

169.  Scientific  classification  of  plants.  —  The  various 
methods  of  grouping  plants  that  we  have  thus  far  considered 
do  not  indicate  real  relationships  among  plants,  for  these 
schemes  call  attention  only  to  certain  superficial  resemblances 


PLANT  CLASSIFICATION  159 

and  differences  in  form,  or  size,  or  habit.  True  scientific 
classification  seeks  to  bring  together  into  a  given  group  all  the 
plants  that  are  closely  related  to  each  other;  that  is,  those 
which  are  probably  descended  from  common  ancestors.  In 
the  first  place,  all  plants  are  divided  into  two  great  groups 
known  as  seed-producing  plants,  and  spore-producing  plants. 
The  first  is  the  group  to  which  most  of  our  attention  has  thus 
far  been  given,  and  it  embraces  the  herbs,  shrubs,  and  trees 
with  which  we  are  most  familiar.  We  should  bear  in  mind, 
however,  that  many  plants,  like  the  palm  and  rubber  plant, 
which  do  not  produce  flowers  in  our  climate,  develop  flowers, 
fruits,  and  seeds  when  they  are  growing  in  their  natural 
home.  Other  plants  with  inconspicuous  flowers  —  for  ex- 
ample, grasses,  elms,  and  pines  —  also  belong  to  this  great 
group  of  seed-producing  plants. 

Sub-kingdom  I,  Seed-producing  Plants   (Optional) 

170.  Gymnosperms   and    angiosperms.  —  Seed-producing  plants 
are  still  further  subdivided  into  two  groups.     The  first  group  includes 
all  plants  like  the  pines,  hemlocks,  and  spruces,  in  which  the  seeds  are 
not  produced  in  ovaries,  but  at  the  base  of  scale-like  leaves  which  are 
usually  grouped  together  to  form  cones;  hence  the  name  cone-bear- 
ing plants,  which  will  apply  to  the  common  forms.     The  whole  group 
is  known  as  gymnospenns  (from  Greek  meaning  naked  seeds). 

Plants  like  beans,  cucumbers,  and  pansies,  on  the  other  hand, 
develop  their  seeds  in  ovaries,  and  these  and  all  other  plants  of  this 
type  constitute  the  second  of  the  two  sub-divisions,  which  is  known 
as  the  angiosperms  (from  Greek  meaning  having  a  vessel  for  seeds). 

171.  Monocotyledons  and  dicotyledons.  —  Again,  the  seed-pro- 
ducing plants  may  be  classified  according  to  the  number  of  coty- 
ledons found  in  the  seed.     The  corn,  gladiolus,  and  lilies,  for  example, 
have  seeds  with  one  cotyledon,  and  hence  these  are  known  as  mono- 
cotyledons    (Greek,  mono  =  one  +  cotyledon).     Beans,    peas,    and 
maples,  on  the  other  hand,  have  two  cotyledons  and  are  therefore 


160 


PLANT  BIOLOGY 


called  dicotyledons  (Greek,  di  =  two  +  cotyledons).  There  are 
other  striking  characteristics  which  distinguish  these  two  groups  of 
angiosperms,  which  have  already  been  brought  out  in  our  laboratory 
work,  as  the  following  table  will  show: 


MONOCOTYLEDONS 
(Corn,  tulip,  gladiolus) 

DICOTYLEDONS 
(Bean,  horse-chestnut, 
pansy) 

Number  of  cotyledons 

one 

two 

Veining  of  leaves 

parallel 

netted 

Stem  structure 

woody  bundles  scat- 

bark,  wood   in    dis- 

tered through  pith 

tinct  annual  rings, 

pith  in  center 

Number    of    stamens 

based    on    plan    of 

based  on  plan  of  five 

and  other  parts  of 

three      or     some 

or    some    number 

flower 

multiple  of  three 

other  than  three 

172.  Plant  families.  —  Continuing  our  classification  of  the  angio- 
sperm  group  still  further,  we  find  that  the  dicotyledons  are  sub- 
divided into  over  one  hundred  and  sixty  so-called  plant  families, 
some  of  which  are  the  violet  family,  the  buttercup  family,  the  rose 
family,  and  the  pulse  family.     This  grouping  into  families  is  based 
largely  upon  flower  structure,  and  so  it  sometimes   happens   that 
an  herb  and  a  tree  belong  to  the  same  family.     For  example,  the 
pea,  bean,  and  the  locust  tree  all  belong  to  the  pulse  family,  since 
they  have  flowers  closely  resembling  each  other. 

173.  Plant  genus.  —  Again,  each  of  the  160  or  more  families 
is  made  up  of  a  varying  number  of  more  closely  related  plant  groups, 
each  of  which  is  known  as  a  genus.     The  rose  family,  for  example, 
has  fourteen  genera,  some  of  which  are  the  pear  genus,  the  rose  genus, 
and  the  cherry  genus.1 

174.  Plant  species.  —  Once  more,  each  genus  consists  of  a  vary- 
ing number  of  species,  the  members  of  which  resemble  each  other 


PLANT  CLASSIFICATION 


161 


very  closely.  The  pear  genus  consists  of  the  pear  species,  the  apple 
species,  and  the  crab  apple  species.  Species,  again,  may  be  still 
further  subdivided  into  varieties,  in  which  the  plants  are  more  closely 
related  (e.g.  Baldwin  and  Greening  varieties  among  apples).  And 
finally  a  species  (or  variety)  is  made  up  of  individual  plants,  that 
resemble  each  other  in  all  essential  respects. 


Sub-kingdom  II,  Spore-producing  Plants  (Optional) 


A.   Ferns 


176.  The  fern  plant  — 
We  turn  now  from  a  dis- 
cussion of  seed-bearing 
plants  to  a  consideration 
of  those  plants  which 
never  produce  flowers  or 
seeds.  As  a  representa- 
tive of  the  highest  group 
of  plants  without  seeds, 
we  will  study  the  ferns. 
The  majority  of  ferns 
grow  in  damp,  shady 
places,  and  among  the 
common  kinds  we  may 
name  the  brake,  the 
maiden-hair,  and  the  rock 
fern.  In  any  one  of  these 
ferns  the  parts  above 
ground  which  are  true 
leaves  are  known  as 
fronds.  The  main  axis 
of  each  frond  runs 
throughout  the  leaf,  and 
to  each  side  are  attached 
the  leaflets,  which  may  or 


FIG.  82.  —  Fern  plant  (Aspidium),  showing 
roots,  rhizome,  and  frond  :  A,  section  of 
fruit  dot  (sorus),  showing  spore  cases,  some 
of  which  are  ejecting  their  spores  ;  B,  por- 
tion of  a  leaflet,  showing  unripe  fruit  dots  ; 
C,  portion  of  a  leaflet,  showing  ripe  fruit 
dots.  —  (Strasburger.) 


162 


PLANT  BIOLOGY 


may  not  be  still  further  subdivided.     Hence,  a  fern  leaf  is  usually 
compound,  and  is  strikingly  graceful  in  its  appearance. 

Beneath  the  ground  the  fronds  grow  from  a  horizontal  stem  called 
the  rhizome,  which  is  more  or  less  enlarged  for  food  storage,  depend- 
ing on  the  kind  of  fern.  To  this  rhi- 
zome are  attached  the  roots  by  which 
the  plant  is  supplied  with  soil-water. 
The  fern  plant,  therefore,  like  seed- 
bearing  plants,  has  all  three  kinds  of 
nutritive  organs  (roots,  stem,  and  leaves), 
and  carries  on  carbohydrate  manufacture 
in  the  green  fronds,  storing  away  the 
food  in  the  rhizome,  since  the  leaves  die 
to  the  ground  each  year.  The  follow- 
ing spring  the  tiny  leaves  push  up 
through  the  ground  from  the  under- 
ground stem,  unrolling  and  spreading 
their  leaflets  from  the  base  to  the  tip. 

176.  Fern  spores.  —  On  the  under 
surface  of  some  of  the  leaflets  of  the 
ferns  named  above  are  little  dots  which 
are  often  brown.  These  are  known  as 
fruit-dots  (son).  Each  fruit  dot,  if  ex- 
amined with  a  microscope,  is  found  to 
consist  of  several  smaller  objects  known 
as  spore-cases.  (B,  C,  Fig.  82.)  When 
these  tiny  spore  cases  are  ripe,  they  open, 
often  with  considerable  force,  and  eject  a 
powder,  each  particle  of  which  is  called 
a  spore.  (Fig.  82,  A.)  Each  spore  con- 
sists of  a  single  cell. 


FIG.  83.  —  Development  of 
fern  plant. 

A,  a  germinating  fern  spore  ; 
B,  a  later  stage  in  germina- 
tion ;  C,  a  full-grown  pro- 
thallus,  showing  rhizoids, 
antheridia  (or  spermaries, 
and  archegonia  (or 
ovaries;  Z>,  section  of 
antheridia  (or  spermary)  ; 
E,  a  sperm  cell ;  F,  a  section 
of  archegonia  (or  ovary) 
containing  an  egg-cell ;  G, 
young  fern  plant  develop- 
ing from  a  fertilized  egg- 
cell  in  an  ovary,  still  at- 
tached to  the  heart-shaped 
prothallus.  —  (Parker.) 


177.  Fern  prothallus.  —  When  the  spores  fall  to  the  ground  and 
conditions  are  favorable,  they  start  to  germinate,  and  each  finally 
produces  a  small  green,  heart-shaped  plant  known  as  a  prothallus 
(Fig.  83,  C).  The  prothallus,  though  tiny,  consists  of  a  great 


PLANT  CLASSIFICATION  163 

number  of  cells,  some  of  which  form  tiny  outgrowths  from  the  under 
surface  like  root-hairs  (called  rhizoids),  which  anchor  the  prothallus 
to  the  soil  and  aid  in  securing  food  materials. 

On  the  under  surface  likewise  of  each  prothallus,  in  the  region 
of  the  rhizoids,  are  minute  organs,  circular  in  appearance,  known  as 
antheridia  (spermaries),  in  which  are  produced  a  large  number  of 
sperm-cells  (Fig.  83,  D,  E).  At  a  little  distance  from  the  antheridia, 
near  the  notch  in  the  prothallus,  are  found  other  somewhat  elon- 
gated bodies  called  archegonia  (ovaries).  In  each  of  these  there  is 
developed  a  special  cell  known  as  the  egg-cell  (Fig.  83,  F). 

178.  Fertilization  of  the  egg-cells.  —  When  the  sperm-cells  are 
ripe,  the  antheridia  or  spermaries   are  ruptured,  and  the  sperm- 
cells  make  their  way  by  a  curious  twisting  motion  toward  the  open- 
ings on  the  archegonia.    A  single  sperm-cell  moves  down  the  tube 
of  each  archegonium,  and  penetrates  the  egg-cell,  and  the  two  nuclei 
unite  in  the  process  of  fertilization.     (See  91.)     From  the  fertilized 
egg-cell  develops  a  fern  plant  composed  of  many  cells  of  various 
kinds,  which  are  all  derived  from  the  fertilized  egg-cell. 

179.  Alternation  of  generations.  —  Thus  we  see  that  in  the  life- 
history  of  the  fern  plant  we  have  two  distinct  generations.     The 
first  is  the  ordinary  fern  plant,  which  is  familiar  to  all,  and  which  is 
known  as  the  asexual  generation  or  spore  generation,  because  the  spores 
formed  on  the  fronds  produce  the  next  generation   (prothallus) 
without  fertilization  or  the  union  of  two  kinds  of  cells.     The  second 
generation,  the  prothallus,  is  the  sexual  generation,  because,  as  we 
have  seen,  it  can  only  produce  a  fern  plant  from  the  fertilized  egg- 
cell.     In  plants  like  the  fern,  in  which  an  individual  (fern)  produces 
another  plant  (prothallus)  unlike  itself,  and  this  in  turn  gives  rise 
to  a  plant  like  the  original  (fern),  we  have  so-called  alternation  of 
generations. 

180.  Suggestions    for    the   study   of    the    fern.  —  No.    65.     If 
this  topic  is  suggested  for  study,  pupils  should  be  encouraged  to 
collect  their  own  material,  noting  the  surroundings  or  habitat  of  each 
kind  of  fern.     They  should  describe  the  location,  form,  and  color 
of  each  of  the  nutritive  organs,  and  of  the  fruit  dots,  and  draw  the 


164  PLANT  BIOLOGY 

entire  fern.  Each  student  should  study  a  prothallus  with  a  hand 
magnifier,  making  an  enlarged  drawing  of  the  same  to  show  its 
form  and  the  position  and  shape  of  the  rhizoids,  antheridia,  and  arche- 
gonia.  A  demonstration  of  the  steps  in  the  life  history  may  well 
be  shown  from  charts. 

B.   Mosses 

181.  The  moss  plant. — A  second   group  of   flowerless   plants 
includes  the  mosses.     In  general,  mosses  are  smaller  plants  than  the 
ferns,  but  like  them  are  usually  found  in  damp,  shady  places.    If 
one  examines  a  moss  plant  when  it  is  "  in  fruit,"  a  slender  stem  will 
be  seen  projecting  from  the  leafy  part  below.     At  the  upper  end 
of  this  slender  stem,  a  covered  cup-like  structure  is  evident  (Fig. 
84,  A,  &).    This  cup,  or  capsule  as  it  is  called,  is  filled  with  tiny  dust- 
like  particles,  which  when  examined  with  a  compound  microscope 
prove  to  be  cells.     They  are  called  spores.     The  spores  are  repro- 
ductive bodies  similar  to  those  produced  in  the  spore  cases  of  ferns. 

182.  The  moss  protonema.  — When   these   bodies  are  ripe,  the 
capsule  opens  and  discharges  some  of  the  spores,  which  fall  to  the 
ground  and  soon  begin  to  grow,  forming  at  first  an  elongated  cell 
(Fig.  84,  H)  which  later  divides,  giving  rise  to  two  cells.     This 
process  continues  until  a  slender,  green,  thread-like  mass  is  formed, 
with  many  branches.     This  thread-like  mass  is  called  the  protonema 
(Fig.  84,  G).     Some  of  the  branches  produce  buds  which  finally 
grow  into  the  leafy  structure  which  we  know  as  the  moss  plant 
(Fig.  84,  B,  A). 

183.  The  sexual  generation  of  the  moss.  —  At  the  top  of  some 
moss  plants  at  certain  seasons  of  the  year,  in  the  midst  of  the  rosette 
of  green  moss  leaves,  may  be  found  tiny  flask-shaped  organs,  the 
archegonia  (ovaries)  (Fig.  84,  F).    At  the  base  of  each  of  these 
organs  is  produced  an  egg-cell.     Sometimes  in  the  same  moss  plant, 
and  sometimes  in  another,  are  to  be  found  club-shaped  organs  called 
antheridia  (spermaries)    (Fig.  84,  E).     In  the  antheridia  are  pro- 
duced sperm-cells   (Fig.  84,   D).    At  the  proper  time  the  sperm- 
cells  make  their  way  into  the  archegonia,  and  when  a  sperm-cell 


PLANT  CLASSIFICATION 


165 


reaches  an  egg-cell  they  fuse,  the  two  nuclei  unite,  and  a  fertilized 
egg-cell  is  formed.    This  fertilized  egg,  by  the  process  of  growth  and 


FIG.  84.  —  Development  of  a  moss  plant. 

A,  moss  plant  with  spore  case  (k)  having  a  lid  (c)  ;  z,  rhizoids ;  B,  young 
moss  plant ;  C,  enlarged  view  of  spore  case,  with  lid  (c)  detached ;  D, 
single  sperm-cell ;  E,  spermary  with  escaping  sperms ;  F,  ovary  with 
dividing  egg-cell  (6)  ;  G,  branching  protonema  ;  H,  spore  germinating  to 
form  protonema. 

cell  division  (Fig.  84,  F,  o),  finally  forms  the  slender  stalk  with  the 
capsule  and  spores  at  the  end  of  it  like  that  referred  to  in  181 
(Fig.  84,  A,  C). 


166  PLANT  BIOLOGY 

184.  Alternation  of  generations  in  the  moss.  —  The  protonema 
and  the  leafy  shoots  with  their  antheridia  and  archegonia  are  known 
as  the  sexual  generation  because  it  is  this  plant  that  produces  eggs 
and  sperm-cells  which  must  unite  before  the  egg  can  develop  into 
the  spore-bearing  plant.  The  slender  stalk  with  the  capsule  at  the 
end  which  is  produced  by  the  fertilized  egg-cell  is  called  the  asexual 
generation,  since  the  spore-bearing  plant  can  reproduce  without  the 
union  of  two  kinds  of  cells.  The  spore- bearing  plant  is  dependent 
oh  the  leafy  plant  for  all  its  food.  In  the  fern,  on  the  other  hand,  it 
is  evident  that  the  spore-bearing  plant  and  the  plant  producing 
eggs  and  sperms  are  entirely  independent  plants.  In  both  of  these 
groups  of  seedless  plants,  however,  there  is  an  alternation  of  genera- 
tions. 

185.  Suggestions  for  the  study  of  mosses.  —  No.  66.  The  teacher 
should  secure  plenty  of  material  for  the  demonstration  both  of 
the  plants  with  spore  cases  and  if  possible  the  plants  with  arche- 
gonia and  antheridia.  On  account  of  its  size  the  pigeon  wheat 
moss  is  desirable.  The  material  may  be  collected  and  dried,  since 
both  generations  are  not  likely  to  be  obtained  at  the  same  time  of 
year.  If  spore  cases  are  on  hand,  the  work  might  then  be  done  when 
the  sexual  plants  can  be  secured  in  a  fresh  condition.  The  pupil 
should  describe  and  draw  the  leafy  moss  plant.  The  location  of 
archegonia  and  antheridia  should  be  stated.  Then  the  spore-bear- 
ing plant  should  be  described,  together  with  the  relation  to  the  sexual 
plant  which  produced  it,  and  the  spore  case  opened  to  show  the  spores. 
The  two  plants  should  then  be  drawn  and  labeled. 

C.   Algce 

186.  Spirogyra.  —  Any  one  who  has  ever  been  in  parts  of  the 
country  where  ponds  or  very  slowly  moving  bodies  of  water  abound 
must  have  noticed  either  at  the  bottom  or  on  the  surface  of  the  water 
a  green,  slimy  mass.  It  is  so  frequently  found  on  the  surface  that  it 
is  called  "  pond  scum."  If  one  examines  a  small  portion  of  this  mass 
even  with  the  naked  eye,  one  will  see  that  it  consists  of  a  great  num- 
ber of  interlacing  threads.  When  looked  at  with  the  compound 


PLANT  CLASSIFICATION 


167 


microscope  each  of  these  threads  is  seen  to  be  a  series  of  cells  joined 
end  to  end.  All  the  cells  are  practically  the  same  in  shape  and 
structure,  however,  so  that  a  study  of  one  will  make  clear  the  struc- 
ture of  all. 

Inclosing  each  cell  there  is  a  thin  cell  wall.  The  first  structures 
one  is  likely  to  notice  within  the  cell  are  the  chlorophyll  bodies. 
In  the  pond  scum  known  as  Spirogyra  the  chlorophyll  is  arranged 
in  spiral  bands,  and  it  is  this  which  has  given  the  plant  its  name 
(Fig.  85,  B).  In  other  fbrms  the  chlorophyll  is  differently  arranged, 


—  chlorophyll  band 


—  nucleus 


'      chlorophyll  band 


FIG.  85.  —  Spirogyra.  —  (Strasburger.) 
A,  two  conjugating  threads  of  Spirogyra  ;  B,  single  cell  of  Spirogyra. 

sometimes  in  star-shaped  masses,  one  in  each  half  of  the  cell,  and 
sometimes  diffused  throughout  the  cell.  If  a  little  iodine  is  added 
to  the  specimen  when  it  is  being  examined  under  the  microscope, 
a  nucleus  may  be  distinguished  near  the  center  of  each  cell  (Fig.  85, 
B}.  In  the  cell-body  and  nucleus  the  protoplasm  appears  as  a 
clear  and  almost  transparent  mass. 


168  PLANT  BIOLOGY 

The  thread  or  filament  continues  to  increase  in  length  by  the 
growth  and  division  of  certain  individual  cells  that  compose  it. 
At  the  close  of  the  season  most  of  the  filaments  perish,  but  some  of 
them  undergo  peculiar  changes.  The  bands  of  chlorophyll  lose  their 
definiteness,  the  protoplasm  becomes  massed,  tiny  outgrowths  from 
the  sides  of  the  cells  occur,  and  these  continue  to  extend  till  they 
meet  similar  outgrowths  from  a  neighboring  filament  (Fig.  85,  A). 
These  outgrowths  unite,  and  thus  a  tube  from  one  cell  to  the  other 
is  formed.  The  contents  of  one  cell  pass  through  to  another,  and 
the  two  masses  fuse.  A  thick  wall  forms  about  the  united  mass  and 
the  old  cell  walls  decay  and  fall  away,  leaving  these  thick- walled 
zygospores  on  the  bottom  of  the  pond.  In  the  spring  the  protoplasm 
within  each  of  these  zygospores  begins  to  grow,  breaks  through  the 
thick  wall,  and  proceeds  to  form  a  new  filament  by  cell  division. 
The  formation  of  the  zygospores  is  known  as  conjugation;  it  is  a 
kind  of  sexual  reproduction,  though  the  two  cells  taking  part  in  the 
process  are  the  same  in  appearance. 

If  one  observes  pond  scum  on  a  sunny  day,  bubbles  will  be  seen 
escaping  from  the  mass.  A  test  of  this  gas  proves  it  to  be  oxygen, 
and  as  we  should  expect,  it  occurs  in  connection  with  the  process  of 
carbohydrate  manufacture  the  same  as  in  other  green  plants.  In 
fact  it  has  been  proved  that  these  simple  plants  manufacture  foods, 
digest,  assimilate,  respire,  and  reproduce  as  do  the  higher  plants 
we  have  studied.  The  differences,  then,  between  a  simple  plant 
like  Spirogyra  and  a  bean  plant  or  an  oak  tree  are  mainly  those  of 
structure  and  adaptations  for  the  performance  of  functions  which 
are  largely  common  to  both.  Indeed,  it  is  evident  that  every  cell 
of  the  Spirogyra  is  in  contact  with  the  water,  from  which  all  the  sub- 
stances needed  are  obtained  by  absorption.  Hence,  any  special 
adaptations  for  securing  food  materials  or  of  giving  off  wastes,  such 
as  are  found  in  higher  plants,  are  unnecessary. 

187.  Suggestions  for  the  study  of  Spirogyra.  —  No.  67.  It  is 
desirable  that  pupils  should  see  the  "  pond  scum  "  in  its  habitat, 
even  if  they  do  not  collect  material  for  work.  The  escape  of  bubbles 
may  be  noticed  at  this  time  or  in  the  laboratory.  The  mass  should  be 
described  as  to  color  and  "  feel,"  and  the  fine  threads  noted  by 


PLANT  CLASSIFICATION  169 

floating  the  mass  in  a  saucer  of  water.  A  filament  should  then  be 
studied  under  the  microscope,  and  the  parts  of  a  single  cell  described, 
and  several  cells  should  be  drawn.  If  fresh  zygospore  material  can 
be  obtained,  this  should  also  be  studied,  and  the  parts  described 
above  noted  and  drawn ;  otherwise  charts  or  pictures  may  be  used. 

188.  Pleurococcus  and  other  algae.  —  Another  and  still  simpler 
form  of  plant  life  is  known  as  Pleurococcus.     It  may  be  readily 
obtained  from  the  trunks  on  the  north  side  of       «,  ^^ 
large  trees.    It  appears  as  a  very  thin  green  layer    ^g»J     A  ^ ; 
closely  adhering  to  the  bark.     If  a  little  of  this 

material  is  scraped   off  and  placed  under  the 

compound  microscope,  it  will  be  found  that  it  is    , 

.       ,  ,  ,.  FIG.  86.  — Pleuro- 

made  up  of  a  large  number  of  tiny  circular  green      coccus.  —  (Sedg- 

cells  which  adhere  to  each   other  more  or  less,      wick    and   Wil- 
since  in  the  process  of  reproduction  one  cell      son^ 
divides  to  form  two,  each  of  which  is  considered  to  be  an  individual 
plant.     Thus  the  whole  mass  is  made  up  of  a  large  number  of 
one-celled  plants. 

The  Spirogyra  and  Pleurococcus  are  only  two  of  a  large  number 
of  simple  plants  known  as  algae.  They  differ  widely  in  form,  but 
none  of  them  develop  roots,  stems,  or  leaves.  Among  the  most 
common  algae  are  the  marine  forms  known  as  sea  weeds,  of  which 
there  are  many  kinds. 

189.  Suggestions  for  the  study  of  Pleurococcus.  —  No.  68.     As 
indicated  above,  material  for  the  study  of  Pleurococcus  may  be 
easily  obtained  by  removing  pieces  of  bark  from  trees  having  a  con- 
siderable quantity  of  this  plant  on  their  surface.     If  collected  in  a 
dry  season,  the  bark  should  be  placed  under  a  bell-jar  with  sufficient 
water  to  make  the  air  moist,  and  allowed  to  stand  for  several  days. 
The  place  in  which  the  Pleurococcus  is  found  should  be  described, 
and  also  the  appearance  of  a  mass  of  the  plants.     Single  cells  should 
then  be  studied  under  the  high  power  of  the  compound  microscope, 
and  the  cell  and  its  contents  described  and  drawn. 

D.   Fungi.     (See  Chapter  IX,  147-166.) 


170  PLANT  BIOLOGY 

III.   SUMMARY  OF  A  CLASSIFICATION  OF  THE  PLANT 
KINGDOM 

Division  I  —  Spore-producing  plants. 
Sub-division  1  —  Fungi      (including     bacteria,     yeast,     molds, 

mushrooms,  rusts,  smuts). 
Sub-division  2  —  Algce  (including  Spirogyra,  Pleurococcus,  and 

sea  weeds). 

Sub-division  3  —  Mosses  and  their  relatives. 
Sub-division  4  —  Ferns  and  their  relatives. 

Division  II  —  Seed-producing  plants. 

Sub-division  1  —  Gymnosperms  (including  pines,   spruces,   hem- 
locks). . 

Sub-division  2  —  Angiosperms,  composed  of : 
Class  I  —  Monocotyledons  (e.g.  corn,  lilies,  gladiolus). 
Class  II  —  Dicotyledons  —  composed  of  160  or  more  families, 

one  of  which  is 

Rose  family  —  composed  of  14  genera,  one  of  which  is  the 
Pear  genus  —  composed  of  3  species,  one  of  which  is  the  — 
Apple   species,  of   which  there  are  many  varieties,  e.g. 
Baldwin,  Greening,  etc. 


YELLOW-BILLED   CUCKOOS  EATING  TENT  CATERPILLARS 

Photographed  from  exhibit  in  Brooklyn  Museum  of  Arts 
and  Sciences,  by  A.  E.  Rueff. 


ANIMAL  BIOLOGY 

CHAPTER   I 
INSECTS 

I.   BUTTERFLIES  AND  MOTHS 

1.  Insect  net.  —  Since  most  butterflies  and  moths  are  more  or 
less  injurious,  at  least  in  their  caterpillar  stage,  boys  and  girls 
should  be  taught  that  they  are  benefiting  their  community  by 
catching  and  killing  these  insects  in  a  painless  manner.     For  this 
purpose  an  insect  net  and  a  poison  bottle  are  necessary.     An  insect 
net  may  be  made  by  securing  a  yard  of  galvanized  iron  wire  (Xo.  3), 
bending  it  in  the  form  of  a  ring  (thus  ft),  and  inserting  the  two  ends 
of  the  wire  in  one  end  of  a  light  wooden  rod  about  three  feet  long. 
To  the  wire  ring  should  be  sewed  a  bag  about  two  feet  deep  made 
of  cheesecloth  or  bobinet  (Fig.  1).     To  catch  a  butterfly  or  other 
insect,  wait  until  it  alights,  then  quickly  place  over  it  the  opening 
of  the  net,  holding  up  the  closed  end  of  the  net  till  the  insect  flies 
to  the  top.     Now  place  beneath  the  insect  the  open  mouth  of  a 
poison  bottle  prepared  as  follows,  and  after  the  insect  is  in  the 
bottle  quickly  replace  the  cover. 

2.  Poison  bottle.  —  Secure  a  pint  fruit  jar  or  a  wide-mouthed 
bottle  fitted  with  a  cover.     Into  the  bottom  put  a  spoonful  of  more 
or    less    pulverized    potassium    cyanide.     Thoroughly    mix    some 
plaster  of  Paris  in  water  and  thus  make  a  thin  paste.     Carefully 
pour  the  liquid  into  the  jar  until  it  forms  a  layer  about  an  inch 
thick.     When  this  hardens,  it  covers  and  holds  the  cyanide  in  place, 
but  it  is  porous  enough  to  allow  fumes  to  escape,  which  kill  most 
insects  in  the  closed  space  in  a  few  moments.     The  bottles  are  per- 
fectly safe  in  the  hands  of  pupils.     Care  should  be  taken,  however, 
not  to  handle  the  cyanide  or  to  breathe  in  the  fumes.     The  bottle 

B  1 


ANIMAL  BIOLOGY 


should  be  kept  tightly  closed  when  not 
in  use,  and  should  be  distinctly  labeled 
"  Poison  Bottle"  (Fig.  2).  If  the  bottle 
is  broken,  the  pieces  of  glass  and  all  the 
contents  should  be  buried  in  the  earth. 

3.  Preparation  of  butterflies  for  study 
or  for  collections.  —  For  laboratory  study 
it  is  desirable  to  use  the  largest  butter- 
flies obtainable.  The  work  will  be  carried 
on  to  much  better  advantage  if  there 
is  at  least  one  mounted  specimen  for 
each  two  pupils.  These  should  be  pre- 
pared with  the  wings  fully  extended, 
with  the  legs  spread  out  as  in  walking, 
and  with  the  proboscis  partly  uncoiled. 
To  get  the  material  in  this  shape  place 
two  books  about  half  an  inch  apart  on 
a  soft  board ;  run  an  insect  pin  through 
the  thorax  of  a  freshly  killed  insect,  ex- 
tend the  legs 
and  proboscis, 
then  put  the 
body  of  the 
insect  between 
the  two  books, 
thrusting  the 

tip  of  the  pin  into  the  board  beneath. 

Spread  out  the  fore  wings  on  the  book 

covers  so  that  their  hind  margins  are  at 

right  angles  to  the  thorax,  pull  the  hind 

wings  outward  into  their  natural  position 

when  at  rest,  and  hold  the  two  pairs  in 

place  with  pieces  of  glass  till  the  specimen     

has  dried.     Butterfly  spreading  boards    FlG.  2.- Poison  bottle  for 


FIG.  1.  —  Insect  net. 


may  be  bought  or  made  (Fig.  3). 


killing  insects. 


INSECTS  3 

Dry  specimens  may  be  relaxed  by  placing  a  quantity  of  sand  or 
crumpled  paper  in  a  battery  jar  or  other  wide-mouthed  receptacle 
that  can  be  tightly  covered.  Wet  the  sand  or  paper  thoroughly 
and  then  sprinkle  over  it  a  little  dry  sand  or  cover  with  blotting- 
paper. 

Put  in  the  dried  butter- 
flies about  twenty-four 
hours  before  they  are  to 
be  spread,  and  cover  the 
dish.  If  the  relaxing  jar 
is  kept  in  a  warm  place, 
the  process  will  be  has-  FIG  3  _  Ingect  spreading  ^^ 

tened,  but  care  should  be 

taken  not  to  leave  the  insects  in  the  moist  chamber  long  enough 
for  mold  to  grow  upon  them.  It  is  of  course  better  to  mount  the 
butterflies  as  soon  as  they  are  killed. 

4.  Insect  boxes.  —  A  box  for  displaying  a  butterfly  for  class 
study  may  be  made  as  described  below  by  any  fourteen-year-old 
boy;  these  cases  will  preserve  the  insects  from  year  to  year,  thus 
saving  labor  as  well  as  insuring  good  material  that  pupils  can 
examine  from  both  sides.  The  boxes  may  likewise  be  used  as  cages 
for  the  study  of  the  activities  of  live  grasshoppers,  caterpillars, 
or  other  insects.  After  butterflies  have  been  studied  they  should 
be  transferred  to  an  insect  case  or  other  moth-proof  box,  a  piece  of 
cotton  soaked  in  carbon  bisulphide  should  be  inserted,  and  the  box 
kept  tightly  closed  till  the  butterflies  are  again  needed.  "  Chiclet  " 
boxes,  since  they  have  glass  covers,  may  be  used  for  storing  and  dis- 
playing the  insect  collections  that  may  be  made  by  pupils.  A  layer 
of  absorbent  cotton  over  the  bottom  of  the  box  makes  a  good  back- 
ground (Fig.  4) . 

To  make  the  insect  boxes,  secure  from  a  mill  or  a  local  carpenter 
strips  of  wood  1\  inches  wide  and  \  inch  thick,  with  grooves  \  inch 
wide  and  \  inch  deep,  cut  a  quarter  of  an  inch  from  the  two  margins 
of  one  side.  About  18  inches  will  be  required  for  each  box.  For  the 
sides  saw  up  two  pieces  each  5£  inches  long,  and  for  the  ends  the 


ANIMAL  BIOLOGY 


INSECTS 


pieces  should  be  3f  inches  in  length.  One  of  the  ends  should  be 
planed  down  to  a  width  of  If  inches  (the  distance  between  the 
grooves).  Nail  the  four  pieces  together  and  insert  in  the  grooves 
on  each  side  a  cleaned  4X5  picture  negative,  the  gelatin  of  which 
may  be  easily  removed  with  hot  water.  Glue  to  the  center  of 
one  of  the  glasses  a  piece  of  cork  to  hold  the  bisect  pin,  and  fasten 
a  piece  of  wood  to  the  narrow  end  by  a  wire  nail,  which  will 
prevent  the  glasses  from  slipping  out  but  will  still  allow  the  box  to 
be  opened.  The  boxes  are  made  more  attractive  if  they  are  treated 
with  dark  oak  jap-a-lac  or  stain  (Fig.  5). 


FIG.  5.  —  Insect  box. 

5.  Experiments  with  living  butterflies.  —  Before  trying  the  feed- 
ing experiments,  the  butterflies  should  be  kept  for  at  least  twenty- 
four  hours  without  food.  After  a  butterfly  has  fed,  it  should  be 
placed  by  itself,  since  the  same  insect  may  be  unwilling  to  eat  a 
second  tune.  Have  as  many  students  at  a  time  see  the  feeding  as 
can  well  do  so ;  this  will  save  time,  and  fewer  butterflies  will  be 
needed.  The  mourning  cloak,  monarch,  and  violet  tip  butterflies 
are  satisfactory  for  this  experiment.  Place  the  butterfly  on  a  stick 
or  other  rough  object,  and  put  the  tiny  drop  of  honey  near  it.  This 
may  be  done  in  a  cage,  or  under  a  glass  jar,  or  in  the  open  laboratory. 


6  ANIMAL  BIOLOGY 

In  the  latter  case  the  windows  should,  of  course,  be  closed,  and  this 
should  also  be  done  while  watching  the  insect  fly.  The  flying  and 
feeding  experiments  with  insects  make  excellent  home  work  if  the 
pupils  can  readily  obtain  the  live  material.  Children  in  New  York 
City  have  caught  and  kept  butterflies  for  several  months,  feeding 
them  twice  or  three  times  a  week. 

6.    Study  of  a  butterfly.  —  Laboratory  study. 

A.  Regions  and  appendages. 

Examine  a  butterfly  and  distinguish  (1)  the  front  or 
anterior  (Latin,  ante  =  before)  region  called  the 
head;  (2)  the  middle  region  called  the  thorax;  and 
(3)  the  hind  or  posterior  (Latin,  post  =  behind) 
region  known  as  the  abdomen. 

1.  Which  region  is  the  smallest?     Which  is  the  widest? 

Which  region  is  longest? 

2.  To  which  region  are  the  appendages  (legs  and  wings) 

attached? 

3.  Which  region  seems  to  have  no  appendages? 

B.  Organs  of  the  head;  feeding. 

1.  Observe  two  long,  slender  appendages  attached  to 

the  head;  they  are  called  antennce  (singular, 
antenna).  State  the  position  of  the  antennae  on 
the  head.  Describe  the  shape  of  an  antenna,  stat- 
ing where  it  is  the  thickest  (i.e.  at  the  proximal  end, 
which  is  next  the  head,  or  at  the  distal  end,  which  is 
farthest  from  its  attachment  to  the  head). 

2.  Near  the  base  or  proximal  end  of  the  antennae  find 

the  large  eyes.  State  their  position  on  the  head, 
their  shape,  and  their  size  (as  compared  with  the 
rest  of  the  head). 

3.  Demonstration.     Take  a  living  or  a  relaxed  specimen 

of  the  butterfly,  and  with  the  help  of  a  dissecting 
needle  find  a  coiled  structure  on  the  lower  or  ven- 
tral surface  of  the  head.  It  is  the  sucking  tube  or 
proboscis.  Gently  uncoil  it  and  describe  this  feed- 
ing organ  as  to  position  and  appearance. 


INSECTS  1 

4.  (Optional  demonstration  or  home  work.)     Place  a  tiny 

drop  of  honey  or  molasses  diluted  with  water  near 
a  butterfly.  If  the  insect  does  not  seem  to  realize 
the  presence  of  the  sweet  substance,  touch  the  pro- 
boscis with  the  needle,  or  if  necessary  put  the  needle 
into  the  coil  of  the  proboscis,  and  gently  unroll  it. 

a.  Describe  what  you  have  done  to  get  the  animal  to  eat. 

6.   Describe  the  movements -of  the  proboscis. 

c.  What  reason  do  you  find  for  supposing  that  the  butter- 

fly is  feeding? 

d.  What  reason  have  you  for  thinking  that  the  proboscis 

must  be  hollow? 

5.  (Optional.)     Between   the   two   antennae,    and   projecting 

upward  in  the  anterior  region  of  the  head,  are  two  slen- 
der structures  covered  with  hair  ;  they  are  the  labial 
palps.  In  some  butterflies  the  labial  palps  are  incon- 
spicuous. If  they  show  hi  your  specimen,  describe 
them  as  to  their  position  and  appearance. 

C.    Organs  of  the  thorax;  locomotion. 

1.  How  many  pairs  of  wings  has  the  butterfly? 

2.  Describe  a  wing  as  to  comparative  length,  breadth, 

and  thickness. 

3.  Hold  a  butterfly  between  your  eyes  and  the  light, 

and  study  carefully  the  course  of  the  veins  in  the 
two  wings  on  one  side.  In  what  region  of  the  wings 
do  the  main  veins  meet? 

4.  Bend  the  veins  and  the  connecting  membrane  in  a 

wing  that  is  given  you. 

a.  Which  is  the  more  rigid? 

b.  What,  then,  is  one  use  of  the  veins? 

5.  Take  a  small  piece  of  the  wing  of  a  butterfly  that  is 

given  you  and  rub  the  surface  with  your  finger  tip. 
a.  Describe  what  you  have  done,  and  state  how  the 
substance  on  your  finger  compares  in  color  with 
the  color  of  the  part  of  the  wing  before  it  was 
rubbed. 


8  ANIMAL  BIOLOGY 

b.  (Optional.)  Shake  some  of  the  powder  from  a  wing  upon 
a  glass  slide  and  examine  it  with  a  low  power  of  the 
compound  microscope.  The  bodies  that  you  see  are 
called  scales.  At  one  end  of  each  scale  you  should 
find  a  tiny  stem  by  which  the  scale  was  attached  to 
the  wing,  and  at  the  other  end  usually  one  or  more 
notches.  Describe  the  shape  of  the  scales  that  you 
are  studying,  and  make  a  sketch  of  one  of  them 
much  enlarged. 

6.  (Optional  home  work.)     Watch  a  butterfly  in  the  field  as  it 

moves  the  wings  in  the  act  of  flying. 

a.  Will  the  downward  stroke  of  the  wings  tend  to  lower  or 

to  raise  the  body? 

b.  What  effect  will  the  upward  stroke  of  the  wings  tend  to 

have? 

c.  In  which  of  these  two  directions,  therefore,  must  the 

butterfly  strike  the  harder  and  more  quickly  in  order 
to  raise  the  body  in  the  air  ? 

d.  Since  the  weight  of  the  body  tends  to  bring  the  animal 

to  the  ground,  in  which  direction  must  the  insect 
strike  with  the  greater  force  in  order  to  keep  itself  at 
a  given  level  in  the  air  ? 

7.  Some  butterflies  have  a  tiny  pair  of  front  legs  that 

are  usually  folded  against  the  thorax ;  so  that 
you  need  to  look  very  carefully  before  deciding 
as  to  the  number  of  legs  present. 

a.  How  many  pairs  of  legs  has  this  insect? 

b.  Are  the  legs  long  and  slender  or  short  and  thick? 

c.  Is  each  leg  all  one  piece  or  is  it  jointed  as  in  the 

human  body? 

d.  Examine  the  lower  end  of  a  leg  and  state  how  the 

foot  is  adapted  for  clinging  to  flowers. 

D.  Make  a  drawing,  natural  size,  of  the  upper  or  dorsal 
surface  of  a  butterfly.  Label  antennae,  eyes, 
proboscis,  head,  thorax,  abdomen,  wings,  prin- 
cipal veins  of  one  wing. 


INSECTS 


9 


Egg  highly 
magnified. 


7.  General  characteristics  of  butterflies.  —  All  butter- 
flies, as  we  shall  see  later,  are  constructed  on  much  the  same 
general  plan  as  that  of  other  insects;  i.e.  their  bodies  are 
divided  into  three  re- 
gions, head,  thorax, 
and  abdomen;  on  the 
head  are  two  antennae 

j  p     i  Egg  on  lower  sur- 

and  a  pair  of  large 
eyes ;  on  the  thorax  are 
two  pairs  of  wings  and 
three  pairs  of  jointed 
legs ;  and  the  abdomen 
is  composed  of  a  num- 
ber of  parts  called  rings 
or  segments  (Fig.  6). 


face  of  milkweed 
leaf. 


Egg  stage. 


Larva  stage  (caterpillar). 


Development  of  pupa  stage. 


8.  Wings  and  their 
scales.  —  While  this 
general  plan  of  struc- 
ture is  common  to  all 
insects,  there  are  cer- 
tain marked  peculiar- 
ities that  enable  one 
readily  to  recognize  a 
butterfly. 

For  instance,  al- 
though other  insects 
have  two  pairs  of  wings, 
no  others  have  these 
organs  so  beautifully  colored  and  relatively  large.  This  color 
of  the  wings  is  due  (we  proved  in  6,  C.  5)  to  tiny  bodies 
called  scales.  If  the  wing  of  a  butterfly  is  rubbed,  the  color 
comes  off  and  the  wing  at  that  point  loses  its  color.  To 


Adult  Stage. 

FIG.  6.  —  Life  history  of  monarch  butter- 
fly.    (Weed.) 


10 


ANIMAL  BIOLOGY 


the  unaided  eye  this  colored  substance  from  the  wing  ap- 
pears to  have  no  definite  form;  in  fact,  it  looks  like  the 
pollen  from  flowers.  An  examination  with  the  compound 
microscope,  however,  shows  that  each 
of  these  tiny  bodies  has  a  definite 
shape  (Fig.  7).  Each  scale  has  at 
one  end  a  tiny  stem,  but  in  other  re- 
spects they  vary  considerably  in  form. 

The  scales  are  attached  in  the  follow- 
ing manner.  In  the  membrane  of  the 
wing  are  openings  into  which  fit  the 
stems  of  the  scales.  The  latter  are 

FIG.   7.  —  Scales   from    arranged  in  rows  and  overlap  some- 
wing  of  a  butterfly.  ,,  .          ,.,          ,,          ,  .      ,  ,, 

thing    like    the    shingles    on    a    roof 

(Fig.   8) .     In  spite  of  this  arrangement  it  is  evident  that  the 
scales  are  not  firmly  attached,  since  the  slightest  touch  is 
sufficient  to  dislodge  many  of  them.     Rough  handling  was 
not  apparently  planned  for  in  the  con- 
struction of  these  insects.     The  pres- 
ence of   these  scales  on  the  wings  of 
butterflies  and  of  their  near  relatives, 
the  moths,   is  so    characteristic  that 
these   insects    have    been    called    the 
Lepidoptera   (Greek,    lepido  =  scale  + 
ptera  =  wings).     Not  only  are   scales 
found  on  the  wings  but,  in  the  shape 
of  hairs,  they   form  a   fuzzy  growth 
over  the  surface  of  the  whole  body.         scales.    (Coleman.) 

9.  Proboscis.  —  Another  marked  characteristic  of  butter- 
flies and  moths  is  the  sucking  tube,  or  proboscis.  While  the 
proboscis  seems  to  be  a  single  structure,  in  reality  it  is  com- 
posed of  two  slender  appendages,  each  having  a  groove  on 


INSECTS  11 

its  inner  surface ;  so  that,  when  the  two  parts  are  brought 
together,  they  form  a  tube  through  which  the  butterfly  sucks 
nectar  from  flowers.  When  the 
proboscis  is  not  in  use,  the  butter- 
fly rolls  it  into  a  tight  coil  under- 
neath the  head  (Fig.  9). 


10.  Legs.  —  The  legs  of  a  but- 
terfly are  not  very   strong,  since 
they  are   relatively  so    long   and 
slender.    This  is  perhaps  the  reason 

why  these  insects  seldom  use  them     FIG.  9.  —  Head  of  butterfly, 
for  walking.     They  are,  however, 

very  useful  in  clinging  to  flowers.  The  two  curved  claws 
on  the  tip  of  each  foot  show  clearly  the  means  by  which 
the  animals  are  able  to  hold  on  to  the  plants  on  which  they 
usually  alight. 

11.  Reproduction  and  life  history  of  butterflies. — As  in 
the  reproduction  of  plants,  the  development  of  the  butterfly 
begins  with  a  special  cell  known  as  an  egg-cell.     These  egg- 
cells  are  formed  in  the  body  of  the  female  insect.     When 
these  egg-cells  have  been  fertilized  by  sperm-cells  from  the 
male  butterfly,  which  correspond  to  sperm-cells  of  the  pollen 
grains  (P.B.1,  91),  the  eggs  are  deposited  on  the  under  side  of 
the  leaves  of  plants  on  which  the  young  can    feed    (Fig. 
6).     These   egg-cells   divide   and  subdivide,  till   at  last  a 
many-celled  organism  is  developed  that  is  commonly  called 
a  "  worm,"  but  that  is  more  correctly  known  as  a  caterpillar 
(Fig.  6). 

The  tiny  caterpillar  emerges  from  the  covering  of  the  egg 
and  begins  to  feed  upon  the  leaf.     As  it  feeds  it  grows,  and 

1  P.  B.  =  "  Elementary  Plant  Biology,"  by  the  authors  of  this  book. 


12  ANIMAL  BIOLOGY 

from  time  to  time  sheds  or  molts  the  more  or  less  hardened 
skin  that  covers  the  whole  insect.  At  last,  after  several 
molts,  the  caterpillar  reaches  its  full  size  and  then  stops 
eating.  At  no  time  in  the  growth  of  the  caterpillar  would 
one  be  likely  to  mistake  it  for  a  butterfly  (Fig.  6).  It  has 
no  wings,  no  antennae,  and  instead  of  a  proboscis  one  finds 
a  pair  of  strong  jaws  with  which  it  eats  leaves.  The  distinc- 
tion between  thorax  and  abdomen  is  not  at  all  clear,  and  at 
first  sight  it  seems  to  have  more  legs  than  a  butterfly.  The 
three  front  legs  are  really  jointed,  but  they  are  so  short  and 
thick  that  there  seems  to  be  no  resemblance  between  them 
and  those  of  a  butterfly.  The  other  pairs  of  legs,  varying 
injiumber,  are  not  jointed  structures,  and  hence  are  not  really 
legs  at  all. 

The  mature  caterpillar  now  attaches  itself  to  some  object 
and,  after  molting  once  more,  usually  assumes  quite  a  different 
shape  from  that  of  the  caterpillar,  and  forms  about  itself 
a  hardened  skin  within  which  a  marvellous  transforma- 
tion occurs  (Fig.  6).  The  long,  coiled  tube  takes  the  place 
of  the  jaws  as  a  feeding  organ,  and  long,  slender,  knobbed 
antennae  appear  on  the  head;  two  pairs  of  beautifully 
colored  wings  develop  on  the  thorax,  as  well  as  the  three 
pairs  of  slender,  jointed  legs  ;  and  at  last  the  fully  developed 
butterfly  breaks  through  the  covering  that  held  it  and  flies 
away. 

It  is  evident,  then,  that  a  butterfly  passes  through  several 
fairly  distinct  stages.  First  we  may  distinguish  the  egg 
stage,  then  the  caterpillar  or  larva  stage,  which  is  followed  by 
the  transformation  stage  in  which  it  is  called  a  pupa.  The 
pupa  of  a  butterfly  is  often  called  a  chrysalis  (Greek,  chrysos 
=  gold)  on  account  of  the  golden  spots  of  color  on  many 
pupa  cases.  Lastly  we  have  the  fully  developed  or  adult 
insect  that  emerges  from  the  pupa  stage. 


INSECTS  13 

12.  Distinguishing  characteristics  of  moths.  —  The  moths  and 
butterflies  belong  to  the  same  order  of  insects;  that  is,  the  scaly 
winged  insects.     But  there  are  some  characteristics  in  which  these 
two  kinds  of  insects  differ.     For  instance,  moths  when  at  rest  fold 
the  wings  horizontally  (Fig.  11),  while  butterflies  fold  them  verti- 
cally, that  is,  erect  (Fig.  10).    The  wings,  too,  of  moths  are  not 
usually  as  brilliantly  colored.     Most  moths  fly  at  night,   while 
butterflies  are  day-flyers.    The  body  of  moths  is  usually  relatively 
broader  than  that  of  butterflies.      Moth  antennae  are  of  various 
shapes,  often  like  a  feather,  but  never  knobbed. 

In  general,  the  life  history  of  moths  is  very  much  the  same  as 
that  of  butterflies,  but  the  larvae  of  many  moths  spin  a  more  or  less 
silky  mass  of  threads  about  themselves,  as  is  the  case  with  the  silk- 
worm caterpillar  (Fig.  16),  and  this  outside  covering  of  the  pupa 
stage  is  known  as  the  cocoon. 

13.  Economic   importance   of   butterflies    and    moths.  — 
The   larvae  of    both    butterflies   and  moths   are  voracious 
feeders,  as  any  one  knows  who  has  had  any  experience  with 
caterpillars.      In  fact,  they  may  be  called  animated  feeding 
machines,  since  the  animal  must  not  only  provide  for  its  own 
growth,  but  must  also  store  up  enough  food  to  form  the  new 
parts  such  as  the  wings  and  the  legs.     Not  all  larvae  of  butter- 
flies and    moths    are   considered    harmful,   however,   since 
some  of  them  are  not  prolific  enough  to  have  any  serious 
effect  upon  vegetation,  which  is  the  source  of  food  of  most 
caterpillars.     This  is  true  of  many  of  the   butterfly  larvae 
and  of  some  moth  larvae.      Then,  too,  some  of  the  larvae 
feed  on  plants  that  are  not  useful  to  man.     This  is  true  of 
the  larva  of  the  monarch  butterfly  (Fig.  6),  which  feeds  upon 
leaves  of  the  milkweed.     The  adult  butterflies  and  moths 
of  course  are  not  capable  of  doing  any  harm  since,  when  they 
eat  anything  at  all,  they  most  commonly  suck  the  nectar 
of  flowers.      When   the   flowers   are   visited   in  this   way, 


14 


ANIMAL  BIOLOGY 


they  are  very  likely  to  be  cross-pollinated  and  thus  are  bene- 
fited instead  of  injured.  But  in  general  the  moths  and 
butterflies  play  but  little  part  in  the  very  important  process 
of  cross-pollination  of  flowers,  most  of  this  work  being  done, 
as  we  shall  soon  learn,  by  the  bees.  The  following  are  a  few 
of  the  injurious  forms  of  butterfly  and  moth  larvae. 

14.    Cabbage  butterfly.  —  This  is  one  of  the  few  forms  of  butter- 
fly larvae  that  are  of  sufficient  economic  importance  to  be  worthy  of 

mention.  Any  one  who  has 
been  near  a  cabbage  patch 
will  remember  to  have  seen 
many  rather  small  white  but- 
terflies (Fig.  10)  hovering 
about  among  the  cabbages. 
These  are  the  cabbage  but- 
terflies depositing  their  eggs 
on  the  under  side  of  the 
leaves.  The  small  green 
caterpillars  that  develop 
from  the  eggs  very  soon  show 
what  they  can  do  in  the  way 
of  eating.  The  ragged  ap- 
pearance of  the  young  leaves 
is  a  warning  to  the  gardener 
to  "get  busy"  if  he  desires 

a  crop.  The  caterpillars  do  most  harm  when  the  cabbages  are 
young,  since  these  plants  may  be  so  injured  as  to  be  unable  to 
form  heads.  The  caterpillars  are  often  killed  by  sprinkling  with 
a  mixture  of  Paris  green  and  arsenate  of  lead  in  water  (47). 
This  mixture  should  not  be  used,  however,  after  the  heads  begin  to 
form,  on  account  of  the  possibility  of  the  poison  collecting  between 
the  leaves  of  the  head,  with  consequent  danger  to  the  consumer. 

16.   Tussock  moth.  —  The  caterpillars  of  the  tussock  moth  attack 
our  shade  trees.    Where  they  are  unchecked,  they  will  practically 


FIG.  10.  —  Life  history  of  cabbage  butter- 
fly.    (Coleman.) 


INSECTS 


15 


strip  the  trees  of  their  leaves.     The  female  moth  is  wingless  (Fig.  11). 
When  she  emerges  from  her  cocoon,  she  lays  a  mass  of  eggs  upon  the 


FIG.  11.  —  Life  history  of  tussock  moth.     (Osborn.) 


outer  surface  of  the  cocoon  and  secretes  about  them  a  white  foamy 
mass  which  hardens  (Fig.  11).     If  this  occurs  in  the  autumn,  the  eggs 


16 


ANIMAL  BIOLOGY 


remain  during  the  winter,  and  the  following  spring  hatch  out.  The 
young  caterpillars  attack  the  leaves  of  the  tree  on  which  they  have 
hatched  out,  or  if  the  cocoon  was  placed  elsewhere,  they  crawl  up 
the  nearest  tree  and  start  business  at  once.  They  are  great  travel- 
ers, and  this  is  the  way  they  spread  through  a  neighborhood,  since, 

as  already  mentioned, 
the  female  cannot  fly. 
To  capture  these  insects 
one  may  place  a  band 
of  cotton  batting  around 
the  trunk  of  each  of  the 
trees  one  wishes  to  pro- 
tect. The  larvse  do  not 
usually  crawl  over  this 
but  will,  if  mature,  pro- 
ceed to  pupate  under- 
neath the  band.  All 
pupae  and  egg  masses 
should  be  collected  (Fig. 
12)  and  burned.  This 
is  about  as  much  as 
the  individual  can  do. 
Where  a  spraying  appa- 
ratus is  available  the 
trees  should  be  sprayed 
with  lead  arsenate,  thus 
killing  all  the  caterpil- 
lars. This  caterpillar  is 
rather  handsome  as  cat- 
erpillars go,  having  a 
bright  red  head  and  a  series  of  yellow  tufts  of  hair  on  the  dorsal 
part  of  the  body  (Fig.  11). 

16.  ,Gypsy  moth  and  brown  tail  moth.  —  The  gypsy  moth  (Fig. 
13)  was  brought  into  Massachusetts  from  Europe  in  1869  in  con- 
nection with  scientific  experiments.  Some  of  these  specimens  acci- 


FIG.  12.  —  Morris  High  School  boys  removing 
63,020  eggs  of  tussock  moth  from  four  trees 
on  school  grounds.  Work  directed  by  Paul 
B.  Mann.  (Photographed  by  Lewis  Enowitz.) 


INSECTS 


17 


L\  manti  ia  dispa 


FIG.  13.  —  Life  history  of   gypsy  moth.      (Prepared  by  Kny-Schecrer  Co. 
Photographed  by  E.  R.  Sanborn,  N.  Y.  Zoological  Park.) 


dentally  escaped  and  gradually  increased  until  the  damage  to  fruit, 
forest,  and  shade  trees  caused  by  the  larvae  was  so  evident  that 
property  owners  had  to  call  upon  the  state  to  aid  in  their  extermina- 


18 


ANIMAL  BIOLOGY 


tion.  Nearly  one  million  dollars  was  expended  during  a  period  of 
ten  years.  At  the  end  of  this  time  the  number  of  the  insects  was  so 
reduced  that  it  was  impossible  to  convince  taxpayers  of  the  neces- 
sity for  further  appropriations  to  complete  the  extermination. 
Since  then  the  gypsy  moths  have  spread  over  the  whole  state  of 
Massachusetts  and  into  the  adjoining  states. 

The  larvse  of  another  moth,  the  brown  tail,  has  likewise  caused 
great  damage  in  the  New  England  states.  The  New  York  State 
Department  of  Education  is  sending  out  colored  pictures  of  the  life 
history  of  both  of  these  insects  with  the  following  statement  regard- 
ing them.  "  Warning  —  Take  Notice.  There  is  grave  danger  of 
both  of  these  dangerous  pests  being  brought  into  New  York  State. 
They  have  destroyed  thousands  of  trees  in  Massachusetts,  and  they 
will  do  the  same  in  New  York  unless  checked.  All  are  hereby  urged 
to  become  familiar  with  the  general  appearance  and  work  of  these 

two  insects,  and  to  report 
anything  suspicious  to  the 
State  Entomologist,  Albany, 
N.Y.,  sending  specimens  if 
possible.  Abundant  hairy 
caterpillars  an  inch  to  two 
inches  long  on  or  in  the 
vicinity  of  defoliated  trees 
should  lead  to  investiga- 
tion." 

17.    Codling   moth. — 

Every  one  has  eaten  into 
apples  that  have  been  in- 
jured by  the  "  apple  worm," 
which  is  the  larva  of  the 

codling  moth  (Fig.  14).   The 
FIG.  14.  —  Life  history  of  codling  moth.        ,  &       / 

(U.  S.  Dept.  of  Agriculture.)  damage   to    the   fruit    crop 

from    this    insect    in    New 

York  State  alone  is  estimated  at  three  million  dollars  each  year. 
According  to  Professor  Hodge  ("  Nature  Study  and  Life  ")  the  cod- 


INSECTS  19 

ling  moth  "  was  early  imported  from  Europe  and  is  now  at  home 
wherever  fruit  is  cultivated  in  this  country  and  Canada,  causing  a 
loss  of  from  25  to  75  per  cent  of  the  apple  crop,  as  well  as  that  of  many 
other  fruits.  In  the  heavy  bearing  years  the  wormy  apples  fall  off 
and  are  discarded,  but  the  great  number  of  apples  serves  to  rear 
enormous  numbers  of  the  worms,  and,  according  to  my  observations 
and  experience,  in  the  off  years,  when  apples  would  be  valuable,  the 
worms  take  the  whole  crop. 

"  The  larva?  change  to  pupae  in  May,  emerge  as  moths  in  late 
May  or  June,  and  lay  their  eggs  for  the  first  brood  in  June.  The 
larvae  generally  crawl  into  the  calyx  cup  of  the  young  apples  and  eat 
their  way  to  the  core,  complete  their  growth  in  about  three  weeks, 
commonly  eat  their  way  out  through  the  side  of  the  apple,  and  either 
spin  to  the  ground  and  crawl  to  the  trunk  of  the  tree  or  crawl  down 
the  branches  and  make  their  cocoons  under  the  bark  again.  This 
occurs  with  the  greater  number  early  in  July.  This  habit  affords 
one  of  the  most  vulnerable  points  of  attack.  To  trap  practically 
all  the  codling'  moths  in  an  orchard  it  is  only  necessary  to  scrape 
all  loose  bark  off  from  the  trees  and  fasten  around  the  trunks  a  band 
of  burlap  or  heavy  paper.  Remove  the  bands  and  collect  all  larvae 
once  a  week  during  July."  The  practice  of  most  commercial  grow- 
ers at  the  present  time,  however,  is  to  depend  very  largely  or  entirely 
on  spraying  with  a  poison  (e.g.  arsenate  of  lead,  47).  One  applica- 
tion, even,  a  week  or  ten  days  after  the  blossoms  fall,  if  thorough, 
will  frequently  give  95  per  cent  to  98  per  cent  of  sound  fruit.1 

18.  Clothes  moths.  — "  The  little  buff-colored  clothes  moths 
(Fig.  15)  sometimes  seen  flitting  about  rooms,  attracted  to  lamps 
at  night,  or  dislodged  from  infested  garments  or  portieres,  are  them- 
selves harmless  enough,  for  their  mouth  parts  are  rudimentary,  and 
no  food  whatever  is  taken  in  the  winged  state.  The  destruction 
occasioned  by  these  pests  is,  therefore,  limited  entirely  to  the  feed- 
ing or  larval  stage.  The  killing  of  the  moths  by  the  aggrieved 

1  The  authors  are  indebted  to  Mr.  E.  P.  Felt,  state  entomologist 
of  New  York,  for  this  and  several  other  suggestions  relating  to 
insects. 


20 


ANIMAL  BIOLOGY 


housekeeper,  while  usually  based  on  the  wrong  inference  that  they 
are  actually  engaged  in  eating  her  woolens,  is,  nevertheless,  a 
most  valuable  proceeding,  because  it  checks,  in  so  much,  the  multi- 
plication of  the  species  which  is  the  sole  duty  of  the  adult  insect. 

"  There  is  no  easy  method  of  preventing  the  damage  done  by 
clothes  moths,  and  to  maintain  the  integrity  of  woolens  or  other 
materials  which  they  are  likely  to  attack  demands  constant  vigi- 
lance, with  frequent  inspection  and  treatment.  In  general,  they  are 

liable  to  affect  injuriously 
only  articles  which  are  put 
away  and  left  undisturbed 
for  some  little  time.  .  .  . 
Agitation,  such  as  beating 
anc*  sna^mS>  or  brushing, 
an<^  exP°sure  to  air  and 
sunlight,  are  old  remedies 
and  still  among  the  best  at 
command.  Various  repel- 
lants,  such  as  tobacco,  cam- 
phor, naphthalene  cones  or  balls,  and  cedar  chips  or  sprigs,  have 
a  certain  value  if  the  garments  are  not  already  stocked  with  eggs 
or  larvae.  .  .  .  Furs  and  such  garments  may  be  stored  in  boxes  or 
trunks  which  have  been  lined  with  the  heavy  tar  paper  used  in 
buildings.  New  papering  should  be  given  to  such  receptacles 
every  year  or  two."  1 

19.  Silkworms.  —  One  species  of  moth,  the  silkworm  (Fig.  16), 
is  of  great  economic  importance  to  man.  .  The  larva  of  this  insect 
feeds  upon  the  leaves  of  the  mulberry  tree,  and  after  reaching  matur- 
ity it  spins  a  cocoon,  requiring  about  three  days  for  its  completion. 
The  silk  is  obtained  by  heating  the  cocoon  in  ovens  to  kill  the  pupa, 
and  then  by  reeling  off  the  silk  and  spinning  it  into  threads.  "  For 
many  hundreds  of  years  the  cultivation  of  the  silkworm  was  con- 
fined to  Asiatic  countries.  It  seems  to  have  been  an  industry  in 

1  Circular  No.  36,  Second  Series,  United  States  Department  of 
Agriculture. 


FIG.  15.  —  Life   history  of   clothes  moth. 
(U.  S.  Dept.  of  Agriculture.) 


INSECTS 


21 


FIG.  16.  —  Life  history  of  silkworm  moth.     (Prepared  by  Kny-Scheerer  Co. 
Photographed  by  E.  R.  Sanborn,  N.  Y.  Zoological  Park.) 


China  as  early  as  2600  B.C.,  and  was  not  introduced  into  Europe 
until  530  A.D.  After  the  latter  date  the  culture  rapidly  increased, 
and  soon  became  prominent  in  Turkey,  Italy,  and  Greece,  and  has 


22  ANIMAL  BIOLOGY 

held  its  own  in  those  countries,  becoming  of  great  importance  in 
Italy.  .  .  .  Japan  to-day  produces  a  very  considerable  proportion 
of  the  world's  supply  of  raw  silk.  Thus  of  the  $41,000,000  spent 
by  the  United  States  for  raw  silk  in  1902,  more  than  $20,000,000 
went  to  Japan."  l  Many  attempts  have  been  made  to  introduce 
this  industry  into  the  United  States,  but  the  experiments  thus  far 
made  have  been  rather  unsuccessful. 

II.   GRASSHOPPERS  AND  THEIR  RELATIVES 
20.    Study  of  the  grasshopper.  —  Laboratory  study. 

A.  Regions  and  appendages.  —  Examine  a  grasshopper  and 

distinguish  the  three  regions  of  the  body  proper : 

(1)  the  front  or  anterior  region  called   the  head; 

(2)  the    middle    region    called    the    thorax;    and 

(3)  the  hind  or  posterior  region  known  as  the  ab- 
domen.    (The    anterior  region    of   the    thorax    is 
covered  by  a  cape  or  collar.) 

1.  Which  region  is  the  smallest?     Which  is  the  widest? 

Which  region  is  the  longest  ? 

2.  Which  region  has  legs  and  wings  attached  to  it? 

3.  Which  region  is  made  up  of  a  number  of  similar  rings 

or  segments? 

B.  Organs  of  the  head;  feeding. 

1.  Notice  two  long,  slender  feelers  on  the  head.     They 

are  known  as  antennce  (singular,  antenna).  State 
the  position  of  the  antennae  on  the  head  and  de- 
scribe their  shape. 

2.  Describe  the  shape  and  position  of  the  large  eyes. 

State  their  relative  size  compared  to  that  of  the 
head. 

3.  (Optional.)     Cut  off  with  a  sharp  knife  a  thin  slice  from  the 

outer  surface  of  one  of  the  large  eyes.     Remove  all 
the  soft,  dark  material  from  the  inside.     Place  the 

1  Bailey's  Cyclopedia  of  Agriculture,  Vol.  Ill,  p.  640. 


INSECTS  23 

cleaned  piece  on  a  glass  slide  and  examine  the  outer 
(convex)  surface  with  the  low  power  of  the  compound 
microscope.  Look  for  the  boundary  lines  of  many 
several-sided  areas.  Each  of  these  areas  is  called  a 
facet.  Each  facet  is  the  covering  of  one  of  the  parts 
of  which  the  compound  eye  is  composed. 

a.  Describe  the  preparation  of  the  slide  for  examination. 

b.  Describe  the  shape  of  each  of  the  facets,  and  make  an  out- 

line drawing  of  three  of  them,  much  enlarged,  to 
show  the  way  in  which  they  fit  together. 

4.  (Optional.)     With  the  aid  of  a  magnifier  look  for  a  tiny  eye 

in  the  middle  of  the  front  part  of  the  head.  There  is 
a  similar  eye  between  each  compound  eye  and  the  an- 
tenna of  the  same  side.  These  eyes  are  simple  eyes. 
Describe  the  simple  eyes  as  to  location,  number,  and 
relative  size. 

5.  Find  the  upper  lip  (labrum)  on  the  lower  anterior 

part  of  the  head.     Describe  its  location  and  shape. 

6.  (Demonstration.)    Raise  the  upper  lip  of  a  large  grass- 

hopper and  find  the  jaws  or  mandibles  beneath  it. 
With  a  dissecting  needle  gently  pry  the  jaws  a 
little  way  apart.  Do  the  jaws  move  from  side 
to  side  or  up  and  down? 

7.  (Optional.)     Find  the  lower  lip  on  the  under  side  of  the  head, 

i.e.  next  to  the  thorax.  It  is  divided  vertically  into 
two  equal  parts.  Attached  to  either  side  are  two 
tiny,  jointed  structures  called  labial  palps. 

a.  Describe  the  location  of  the  lower  lip  (labium). 

b.  Describe  the  position  and  appearance  of  the  labial  palps. 

8.  (Optional  demonstration.)     Between  the  jaws  and  the  lower 

lip  of  a  large  specimen  find  a  pair  of  appendages  each 
of  which  is  made  up  of  three  parts  that  are  joined 
together  at  the  base :  (1)  on  the  outside  is  a  several- 
jointed  feeler  or  maxillary  palp;  (2)  next  is  a  spoon- 
shaped  body;  and  (3)  a  curved  and  sharp-pointed 


24  ANIMAL  BIOLOGY 

body.  It  will  be  necessary  to  pull  sideways  on  the 
mouth  parts  to  see  this  inner  part.  These  three 
parts  form  one  appendage  called  the  maxilla  (plural 
maxillce),  or  helping  jaws. 

When  you  have  found  these  three  parts  of  a  maxilla, 
describe  them. 

9.  (Demonstration  or  home  work.)     Place  several  grass- 

hoppers in  a  cage  or  a  glass  jar  with  moistened 
leaves  of  clover,  grass,  or  lettuce.  If  these 
insects  refuse  to  eat,  try  others  till  you  find 
some  that  will  eat. 

a.  Describe  the  movements  of  the  head  and  also  the 
movements  of  the  mouth  parts  while  the  grass- 
hopper is  eating. 

6.  Which  mouth  parts  must  do  most  of  the  biting 
of  the  leaf?  Give  reason. 

10.  (Optional.)     Make  a  drawing,  at  least  four  times  natural 

size  (X  4)  of  the  face  view  of  a  grasshopper.  Label 
antenna,  compound  eye,  simple  eye,  upper  lip. 

C.    Organs  of  the  thorax ;  locomotion. 

1.  How  many  legs  has  a  grasshopper?     Which  pair  is 

the  largest? 

2.  Make  a  sketch  ( X  4)  to  show  the  following  parts  of 

one  of  the  hind  legs :  (1)  a  large  segment 
nearest  to  the  thorax,  the  thigh  or  femur; 

(2)  the  next  segment  to  the  femur,  the  tibia; 

(3)  the  part  that  rests  on  the  ground  when  the 
insect  walks,  the  foot  or  tarsus.     Use  a  magnifier 
to  see  the  several  segments  in  the  tarsus,  the 
little  claws  at  the  tip  end.  and  a  little  pad  be- 
tween the  claws.     Label  femur,  tibia,  segments 
of  the  tarsus,  claws,  pads. 

3.  (Optional.)     Make  a  sketch  (X  4)  of  one  of  the  smaller  legs 

to  show  the  size  and  shape  of  the  parts.  Use  the 
same  labels  as  in  the  drawing  of  the  hind  leg. 


INSECTS  25 

4.  Get  a  grasshopper  to  climb  up  a  stick  or  piece  of  grass. 

a.  Tell  what  you  have  done  and  observed. 

b.  How  is  the  insect  able  to  cling  to  the  stick? 

5.  (Demonstration  or  home  work.)     Place  a  lively  grass- 

hopper in  a  clear  space  on  the  floor  or  in  a  cage. 
Get  it  to  jump  enough  times  to  determine  the 
following  points :  — 

a.  What  is  the  position  of  the  parts  of  the  hind  legs 

when  the  animal  is  ready  to  leap? 

b.  What  is  the  position  of  the  parts  of  the  hind  leg 

the  instant  the  insect  lands? 

c.  What  does  the  grasshopper  do  to  get  ready  for 

another  jump? 

d.  What  movement  throws  the  insect  into  the  air? 

Is  this  movement  made  slowly  or  quickly? 

e.  In  what  respects  are  the  hind  legs  better  fitted 

for  jumping  than  are  the  two  other  pairs? 
/.    What  seems  to  be  the  use  of  the  smaller  pairs  of 
legs  when  the  insect  lands  on  plants? 

6.  Move  the  outer  wings  sideways  and  forwards  at  right 

angles  to  the  body  so  as  to  expose  the  under  pair. 
Spread  out  or  unfold  the  under  wings.  (It  is 
an  advantage  to  mount  the  specimens  on  cork 
and  pin  the  wings  in  the  position  named  above.) 

a.  Which  pair  of  wings  is  better  fitted  for  flying? 
Why? 

6.  How  are  the  outer  wings  fitted  to  protect  the  under 
wings? 

c.  (Optional.)  Draw  (X  2)  the  outline  of  a  front  wing  and 
of  a  hind  wing,  and  sketch  in  the  principal  veins. 
Label  front  wing,  hind  wing,  veins. 

D.   Organs  of  the  abdomen ;  breathing. 

1.  You  will  observe  that  each  of  the  rings  or  segments 
of  the  abdomen  is  composed  of  an  upper  or 
dorsal  half  and  an  under  or  ventral  half.  Make 
a  sketch  ( X  4)  of  a  side  view  of  four  or  five  seg- 
ments of  the  abdomen  to  show  the  structures 
mentioned  above. 


26 


ANIMAL   BIOLOGY 


2.  Secure  an  active  grasshopper,  put  it  in  a  live  cage, 

and  watch  the  movements  of  the  upper  and 
lower  halves  of  the  abdominal  segments.  De- 
scribe what  you  have  observed. 

3.  In  each  segment,  except  those  at  the  tip  of  the  ab- 

domen, there  are  two  breathing  pores  or  spiracles, 
one  on  each  side.  With  the  aid  of  a  magnifier 
look  for  these  breathing  pores  near  the  lower 
margin  of  the  dorsal  half  of  each  segment. 
When  you  have  found  the  spiracles  in  four  or 
five  segments,  show  them  in  your  sketch  (1, 
above),  and  label  breathing  pores  or  spiracles. 

4.  The  spiracles  lead  into  tiny  elastic  breathing  tubes  or 

trachece  (singular  trachea)  which  extend  through- 
.  out  all  parts  of  the  body  of  the  insect  even  into 
the  wings.  The  veins  that  you  can  see  in  the 
wings  contain  these  minute  tubes.  Describe 
the  tracheae  and  state 
their  extent  and  their 
connection  with  the 
spiracles  (Fig.  17). 

5.  The  tracheae  have  an  elastic 

material  in  their  walls, 
so  that  when  they  have 
been  compressed,  they 
will  spring  back  to 
their  former  shape  and 
size  as  soon  as  the 
pressure  is  removed. 
Describe,  now,  the 
structure  of  one  of  the 
air  tubes,  and  state 
what  action  this  struc- 
ture makes  possible. 

6.  When  the  under  or  ventral 

half  of  the  abdomen  moves  up  into  the  dorsal 
half  — 

a.   Will  the  diameter  of  the  abdomen  be  increased  or 
decreased  ? 


FIG.  17.  —  Air  tubes  (tracheae) 
of  an  insect. 


INSECTS  27 

b.  Will  the  air  tubes  be  made  larger  or  smaller? 

Why? 

c.  Will  the  air  now  rush  into  the  air  tubes  or  out  of 

them?     Why? 

7.   If  the  upper  and  lower  halves  of  the  abdomen  now 
move  apart  — 

a.  Will  the  diameter  of  the  abdomen  be  increased  or 

decreased  ? 

b.  How  will  this  movement  affect  the  size  of  the 

tracheae?     Why? 

c.  Will  the  air  now  move  into  the  trachea?  or  out 

through  the  spiracles?     Why? 

21.  Characteristics  of  grasshoppers.  —  After  studying 
two  or  three  insects,  the  student  will  see  that  they  all  re- 
semble the  grasshopper  (1)  in  having  three  regions  of  the 
body  (head,  thorax,  and  abdomen),  (2)  in  possessing  as 
appendages  one  pair  of  antennae,  one  pair  of  compound  eyes, 
two  pairs  of  wings,  and  three  pairs  of  legs,  and  (3)  in  having 
an  abdomen  made  up  of  a  number  of  rings  or  segments. 
The  most  distinguishing  character- 
istics of  the  grasshopper  and  its  rela- 
tives are  found  in  its  mouth  parts 
and  wings.  Grasshoppers  have  bit- 
ing mouth  parts  throughout  their 
life.  These  consist  of  (1)  an  upper 
lip  that  is  notched,  (2)  a  pair  of 
horny  jaws,  or  mandibles,  (3)  a  pair 
of  rather  complicated  helping  jaws  or 
maxillae,  and  (4)  a  lower  lip.  The  two 
lips  move  up  and  down  while  the  two  FlG-  18.  — Mouth  parts  of 

a    cockroach.        (Parker 

pairs  of  jaws  move  from  side  to  side.       ana  Hasweii.) 

All  these  structures  are  well  adapted 

for  holding  and  biting  off  leaves  of  grass  or  other  plants, 

and  this  seems  to  be  the  main  business  of  this  insect. 


28  ANIMAL  BIOLOGY 

Grasshoppers,  too,  are  admirably  provided  with  organs 
of  locomotion.  In  fact,  they  derive  tho>r  name  from  the  ex- 
traordinary feats  of  jumping,  which  they  accomplish  largely 
by  their  long  and  muscular  hind  legs.  If  a  boy  could  jump 
twenty  times  the  length  of  his  legs,  that  is,  a  distance  of  50 
feet,  he  would  make  an  athletic  record  corresponding  to  that 
of  the  common  red-legged  locust.  For  the  hind  legs  of  an 
ordinary  specimen  of  this  insect  are  about  2  inches  long, 
and  they  frequently  leap  4  feet.  The  wings  are  also  of  great 
assistance  in  enabling  the  animal  to  secure  its  food  or  to 
escape  its  enemies.  Flight  is  accomplished  by  the  help  of 
the  hind  pair  only,  and  when  these  are  not  in  use,  they  are 
folded  like  a  fan  beneath  the  outer  pair. 

22.  Life  history  of  the  grasshopper.  —  The  male  grass- 
hopper may  be  easily  distinguished  by  the  rounded  tip  of 
the  abdomen;  the  abdomen  of  the  female,  on  the  other 
hand,  has  at  its  posterior  extremity  four  movable  parts  which 
constitute  the  egg-laying  organ  or  ovi- 
positor (Fig.  19).  The  eggs  are  pro- 
duced within  the  body  of  the  female 
insect.  Before  these  eggs  can  develop, 
however,  each  must  be  fertilized  by 
a  sperm-cell  produced  by  the  male 
grasshopper,  just  as  an  egg-cell  of  a 
plant  must  be  fertilized  by  the  sperm- 
nucleus  of  a  pollen  grain  (P.  B.,  91). 
After  the  process  of  fertilization  has 
FIG.  19. —  Grasshopper  taken  place,  the  female  grasshopper 

laying  eggs.     (Riley,  U.  ^  .       '  ' 

S.Dept.  of  Agriculture.)     (usually  in  the  fall  of  the  year)  bur- 
rows a  hole  in  the  ground  by  alter- 
nately bringing  together,  pushing  into  the  earth,  and  then 
spreading   apart,    the  four  projections  that  make   up   the 


INSECTS 


29 


ovipositor  (Fig.  19).  From  20  to  40  small,  banana-shaped 
eggs  are  then  laid  in  the  bottom  of  the  hole.  In  the  spring 
each  egg  hatches  into  a  tiny  grasshopper,  which  much  re- 
sembles the  adult,  except  that  it  has  no  wings  and  its  head  is 
relatively  large  in  comparison  with  the  rest  of  the  animal. 
The  insect  begins  at  once  to  feed  and  grow,  but  since  its 
whole  exterior  is  hard  and  resistant,  growth  can  only  take 
place  after  this  outer  covering  has  been  split  and  the  insect 
has  crawled  out.  This  process  is  known  as  molting,  and  takes 
place  five  or  six 
times  during  the 
life  history  of  the 
animal.  The  insect 
then  forms  a  new 
and  larger  coat. 

At    each    molt    the     FlG<  20.  — Stages  in  life  history  of  a  grasshopper. 

wings  become  more 

fully  developed,  until  at  the  last  molt  the  adult  insect 
is  produced  (Fig.  20).  Hence,  in  the  life  history  of  the 
grasshopper  there  are  three  more  or  less  distinct  stages : 
(1)  the  egg,  (2)  the  developing  insect,  which  is  known 
as  the  nymph,  and  (3)  the  adult  grasshopper.  This  suc- 
cession of  changes  in  a  life  history  is  known  as  meta- 
morphosis (Greek,  meta  =  one  after  another  +  morphos  = 
form).  But,  because  in  the  development  of  the  grasshopper 
these  changes  are  not  so  striking  as  those  that  occur  in  the 
life  history  of  the  butterfly  (11),  the  metamorphosis  of  the 
grasshopper  is  said  to  be  incomplete.  It  is  better,  however, 
to  refer  to  it  as  a  direct  metamorphosis,  that  of  the  butter- 
fly being  known  as  an  indirect  metamorphosis.  After  reach- 
ing the  adult  stage  and  depositing  eggs,  the  adult  insects  die. 
Only  a  few  of  the  immature  grasshoppers  survive  the  winter, 
and  these  are  the  grasshoppers  that  are  seen  early  in  Spring. 


30 


ANIMAL  BIOLOGY 


23.  Economic  importance  of  grasshoppers.  —  Our  laboratory 
study  of  a  grasshopper's  mouth  parts  and  our  observations  of  its 
methods  of  feeding  have  shown  that  these  insects  resemble  cater- 
pillars, first,  in  having  biting  mouth  parts  (Fig.  18),  and  second,  in 
being  voracious  eaters.  Hence,  as  we  should  expect,  a  large  number 
of  grasshoppers  in  a  given  area  would  mean  a  considerable  destruc- 
tion of  plant  life.  Many  "  plagues  of  locusts  "  (for  grasshoppers 
are  more  correctly  known  as  locusts)  have  been  recorded  in  history. 
One  of  the  first  is  that  recorded  in  the  Bible,  which  occurred  before 
the  departure  or  "  Exodus  "  of  the  Children  of  Israel  from  Egypt. 
"  And  they  (the  locusts)  did  eat  of  every  herb  of  the  land,  and  all  the 
fruit  of  the  trees  .  .  .  and  there  remained  not  any  green  thing  in 
the  trees,  or  in  the  herbs  of  the  field  throughout  all  the  land  of 
Egypt."  (Ex.  x.  15.) 

In  our  own  country  during  the  years  1866  to  1876  there  were 
several  plagues  of  locusts  in  the  grain-producing  states  of  the  West, 

notably  in  Kansas  and  Nebraska. 
The  Rocky  Mountain  grasshoppers 
during  these  years  migrated  in  such 
numbers  that  the  sky  was  dark- 
ened during  their  flight,  and  the 
result  of  their  devastation  was  as 
serious  as  that  described  in  Exo- 
dus. According  to  one  authority 
this  species  of  insect  destroyed 
$200,000,000  of  crops  in  the  west- 
ern states  in  the  space  of  four 
years.  No  great  migrations  have 
occurred  since  1876. 

Locusts  have  been  used  as  food, 
and  even  at  the  present  day  they 
are  commonly  eaten  by  the  Ara- 
bians. In  the  Bible,  it  is  related 
of  John  the  Baptist,  that  while 

preaching  in  the  wilderness  "  he  did 
FIG.  21.  —  Four  walking  sticks  on 

a  branch.    (Coleman.)  eat  of   locusts  and  wild  honey." 


INSECTS  31 

24.  Relatives   of  the   grasshopper.  —  Other  insects  that  have 
structure,  habits,  and  Me  history  similar  to  those  of  the  grasshopper 
are  the  crickets,  cockroaches,  katydids,  and  walking  sticks. 

The  cockroaches  are  more  commonly  known  in  New  York  City 
as  "  Croton  bugs  "  from  the  fact  that  they  frequent  places  close  to 
water  pipes  through  which  Croton  water  is  carried.  They  are  very 
fast  runners,  as  any  one  knows  who  has  tried  to  catch  them,  and 
their  bodies  are  so  thin  that  they  can  easily  hide  away  in  narrow 
cracks.  Their  sharp  jaws  enable  them  to  feed  upon  dried  bread 
and  other  hard  food  (Fig.  18) . 

Katydids  and  walking  sticks  are  striking  examples  of  protective 
resemblance;  that  is,  they  resemble  their  surroundings  in  form  or 
color  so  closely  that  they  may  secure  protection  from  their  enemies 
by  this  means  (Fig.  21). 

III.    BEES   AND   THEIR   RELATIVES 

25.  A  study  of  the  bumblebee.  —  (Laboratory  study.) 

A.   General  survey. 

1.  Give  the  names  of  the  regions  that  you  find  in  the 

body  of  the  bee.     (See  20,  A.) 

2.  State  the  number  and  situation  of    the  antennae. 

(See  20,  B.) 

3.  How  many  compound  eyes  are  present,  and  where 

are  they  situated?     (See  20,  B,  3.) 

4.  (Optional.)    With  the  help,  of  a  magnifier  look  for  the  simple 

eyes  on  the  top  of  the  head  and  between  the  com- 
pound eyes.  How  many  simple  eyes  are  there,  and 
what  is  their  color?  (See  20,  B,  4.) 

5.  Examine  the  legs  and  state  — 

a.  Their  number,  and  the  region  of  the  body  to  which 

they  are  attached. 

b.  The  relative  size  of  the  different  pairs. 

c.  Their  adaptations  (by  structure)  for  walking. 


32  ANIMAL   BIOLOGY 

6.  Examine  the  wings  and  state  — 

a.  Their  number,  and  the  region  of  the  body  to  which 

they  are  attached. 

b.  Their  characteristics  of  texture. 

c.  Their  adaptations  for  flying. 

7.  Is  the  abdomen  segmented  or  not  ? 

B.    Food-getting  organs. 

1.  If  the  mouth  parts  do  not  project  from  the  lower  part 

of  the  head,  you  should  find  them  bent  back- 
ward beneath  the  head  and  thorax.  Use  the 
dissecting  needle  to  straighten  them  out. 
Carefully  separate  these  mouth  parts  and  count 
them. 

a.  How  many  mouth  parts  do  you  find  ? 

b.  Describe  the  general  shape  of  all  these  parts. 

c.  How  are  the  mouth  parts  fitted  to  enable  the  bee 

to  get  nectar  from  flowers  ? 

2.  (Optional.)     Spread  the  mouth  parts  on  some  white  blotting 

paper  and  stick  pins  into  the  blotting  paper  so  as  to 
keep  the  parts  from  coming  together.  Use  the  magni- 
fier to  distinguish  the  following  parts  :  — 

a.  The  central,  longest  part,  the  tongue.     (It  has  hairs  on 

its  surface.)  The  tongue  springs  from  a  broader 
body,  the  lower  lip. 

b.  Two  shorter  parts  on  either  side  of  the  tongue,  springing 

also  from  the  lower  lip,  and  called  labial  palps  be- 
cause they  are  believed  to  correspond  to  the  jointed 
bodies  of  that  name  attached  to  the  lower  lip  of  the 
grasshopper  and  other  insects.  (See  20,  B,  7.) 

c.  Two  broader  parts  springing  from  a  point  farther  back 

than  the  labial  palps  and  supposed  to  correspond  to 
the  helping  jaws  of  the  grasshopper,  and  hence  called 
maxiUcB.  (See  20,  B,  8.) 

Draw  a  front  view  of  the  outline  of  the  head  and  of  these 
five  mouth  parts  (  X  4).     Label  each  part. 


INSECTS  66 

3.  (Optional.)     The  bee  also  has  a  pair  of  small  mandibles. 

They  are  attached  to  the  head  below  the  compound 
eyes.  They  extend  forward  and  are  often  crossed 
underneath  the  lower  lip.  Separate  them  carefully 
with  the  dissecting  needle.  When  the  bee  uses  them, 
it  bends  the  other  mouth  parts  back  out  of  the  way. 

a.  Are  the  mandibles  hard  or  soft? 

b.  Describe  their  color  and  shape. 

Note.  —  The  honeybee  uses  the  mandibles  in  forming 
the  wax  cells  of  the  comb,  and  also  at  tunes  as  organs 
of  defense. 

4.  Examine  the  hind  leg  and  find  the  following  parts  :  — 

a.  A  fairly  prominent  segment  nearest  the  thorax, 

the  femur; 

b.  A  segment  larger  than  the  femur  and  just  below 

it,  the  tibia; 

c.  A  broad  segment  below  the  tibia,  the  basal  part 

of  the  foot  or  tarsus; 

d.  The  remainder  of  the  tarsus  or  foot  consisting  of 

four  tiny  segments  with  hooks  on  the  end 
segment. 

Make  a  drawing  of  one  of  the  hind  legs  ( X  4)  to 
show  all  these  parts  in  outline  and  label  femur, 
tibia,  basal  part  of  tarsus,  hooks,  tarsus. 

5.  Examine  the  outer  surface  of  the  tibia  with  a  magnifier, 

noticing  several  rows  of  hairs  around  the  margin. 
The  portion  of  the  tibia  that  faces  outward, 
together  with  the  hairs,  is  called  the  pollen 
basket. 

Locate  the  pollen  basket  and  show  how  it  is 
adapted  for  holding  pollen. 

u"2(f  History  of  beekeeping.  —  "'  It  is  abundantly  evident  from 
the  records  of  the  remote  past  that  beekeeping  has  always  been  a 
favorite  occupation  with  civilized  nations.  Egypt,  Babylon,  As- 
syria, Palestine,  Greece,  Rome,  and  Carthage  all  had  their  bee- 
keepers. ...  In  the  days  of  Aristotle  (in  Greece)  there  are  said  to 


34 


ANIMAL  BIOLOGY 


have  existed  two  or  three  hundred  treatises  on  bees,  so  that,  then  as 
now,  beekeeping  was  a  favorite  topic  with  authors.  More  books 
have  appeared  on  bees  and  bee-culture  than  have  ever  been  published 
about  any  domestic  animal,  not  excepting  the  horse  or  the  dog."  1 

Yet  from  the  earliest  times  until  the  middle  of  the  last  century 
there  was  little  improvement  in  the  method  of  keeping  bees.  They 
were  allowed  to  build  their  combs  in  hollow  trunks  of  trees  or  in 

hives  so  constructed 
that  it  was  impos- 
sible to  control  in 
any  way  the  work  of 
the  bees  (Fig.  22). 
In  1852,  however, 
Rev.  Lorenzo  Lang- 
stroth  of  Philadel- 
phia invented  a  hive 
with  mo  vable 
frames,  and  his  in- 
vention wholly  rev- 
olutionized the  bee- 
keeping industry. 


FIG.  22.  —  Old  type  of  beehive.  (From  Inter- 
national Encyclopedia.  Dodd,  Mead  &  Co., 
N.  Y.) 


Practically  all  mod- 
ern hives  through- 
out the  world  are  constructed  on  the  plan  that  he  introduced, 
which  is  essentially  as  follows.  In  a  rectangular  box  are  sus- 
pended eight-  to  ten  movable  frames,  in  each  of  which  the  bees 
build  their  comb,  store  honey,  and  develop  their  young;  for 
this  reason  this  part  of  the  hive  is  known  as  the  brood  chamber. 
(One  of  these  frames,  covered  with  bees  is  shown  in  Fig.  23.) 
As  the  season  advances,  the  beekeeper  places  above  the  brood 
chamber  successive  supers  (Latin,  super  =  above),  each  supplied 
with  little  boxes  (Fig.  23)  which  when  filled  with  honeycomb 
usually  weigh  about  a  pound.  It  is  this  excess  of  stored  honey 
that  is  commonly  offered  for  sale. 


1  Cyclopedia  of  American  Agriculture,  Vol.  Ill,  p.  278. 


INSECTS 


35 


27.  Characteristics  and  functions  of  the  queen  and  the 
drones.  —  Honeybees,  though  smaller  than  bumblebees, 
resemble  them  in  their  general  plan  of  structure;  that  is, 
both  kinds  of  insects  have  a  head,  thorax,  and  abdomen,  all 


FIG.  23.  —  Modern  type  of  beehive. 

more  or  less  covered  with  hair,  and  on  the  thorax  are  two 
pairs  of  membranous  wings  and  three  pairs  of  jointed  legs. 
In  every  colony  of  bees  there  is,  except  at  rare  intervals, 
only  one  queen.  The  queen-bee  (Fig.  24)  can  be  readily 
distinguished  from  all  the  other  individuals  in  the  hive  by 
her  long,  slender  abdomen  (Fig.  24).  It  is  her  sole  busi- 


36  ANIMAL  BIOLOGY 

ness  to  deposit  an  egg  in  each  of  the  various  wax  cells  of  the 
brood  chamber.  Queens  have  been  known  to  lay  3000  eggs 
in  a  single  day,  and  since  a  queen  may  live  as  long  as  five 
years,  she  may  lay  over  1,000,000  eggs  during  a  lifetime. 
The  queen  is  therefore  the  mother  of  all  the  bees  in  a  colony. 
The  distinguishing  characteristics  of  drone  or  male  bees 
(Fig.  24)  are  their  broad  abdomens,  the  absence  of  a  sting, 
and  their  very  large,  compound  eyes,  which  nearly  meet 
on  the  top  of  their  heads.  In  numbers  they  vary  at  different 


FIG.  24.  —  Drone,  queen,  and  worker  bee. 

times  of  the  year,  but  during  the  summer  there  are  usually 
400  to  800  in  a  hive. 

We  learned  in  our  study  of  reproduction  in  plants  that 
egg-cells  will  not  develop  into  seeds  unless  they  are  fertilized 
by  sperm-cells  of  pollen  grains.  Now  in  a  beehive,  an  egg 
will  never  develop  into  a  queen-bee  or  a  worker  unless  it 
likewise  is  fertilized  by  a  sperm-cell.  The  drones  or  male 
bees  supply  these  necessary  sperm-cells.  From  the  unfer- 
tilized eggs,  which  a  queen  may  lay,  develop  only  drone  bees. 
In  this  respect  these  egg-cells  of  bees  are  strikingly  different 
from  those  of  plants  and  of  most  animals. 

It  is  clear  from  the  foregoing  account  that  the  queen  and 
drones  carry  on  the  reproductive  functions  of  the  colony,  for 
they  are  specially  adapted  to  increase  the  number  of  bees 
in  a  hive.  To  the  workers,  on  the  other  hand,  as  we  shall 
now  see,  belong  most  of  the  nutritive  functions  of  the  colony. 


INSECTS 


37 


28.  Characteristics  of  worker  bees.  —  While  the  workers 
are  smaller  than  either  the  queen  or  the  drones,  they  are  by 
far  the  most  numerous,  there  being  as  many  as  50,000  in  a 
good  colony  in  midsummer.  In  shape  they  resemble  the 
queen,  as  one  would  expect,  since  they  are  undeveloped 
female  bees.  As  was  the  case  with  the  bumblebee,  their 
mouth  parts  are  very  complicated,  consisting  of  a  central 
tongue  and  two  other  pairs  of  appendages,  all  of  which  form 
a  hollow  tube  for  sucking  up  the 
nectar  of  flowers  (Fig.  25).  Above 

the    tongue    is  a 

pair  of  horny  jaws 

that    move   from 

side  to  side,  which 

the  bees  use  main- 
ly for  comb  build- 
ing. On  the  tibia 

of  each  hind  leg 

of  a  worker  bee  is 

likewise  a  fringe  of 

stiff  hairs,  which, 

together  with  the 

concave  outer  sur- 


FIG.  25.  —  Mouth  parts 
of  a  bee. 


FIG.  26.  —  Hind  leg  of  bee 
with  pollen,  inner  surface. 


face  of  the  tibia,  forms  a  pollen  basket  similar  to  that  of 
the  bumblebee.  In  this  the  insect  gathers  a  mass  of  pollen 
which  may  easily  be  seen  when  the  workers  are  returning  to 

the  hive  (Fig.  26). 


29.  Comb  building.  —  All  the  work  of  comb  manufacture  is 
carried  on  by  the  worker  bees,  and  when  one  studies  this  process 
carefully,  it  is  found  to  be  one  of  the  greatest  marvels  of  animal 
activity.  The  cells  of  the  comb  are  built  out  horizontally  from  each 
side  of  a  central  partition  in  a  brood  frame  or  of  a  super  box.  To 


38 


ANIMAL  BIOLOGY 


save  the  bees'  time  and  to  insure  even  comb,  beekeepers  usually 
insert  in  the  frames  or  honey  boxes  thin  sheets  of  wax  "  foundation  " 
on  which  the  bases  of  the  cells  have  been  impressed  by  machinery. 
Upon  this  the  workers  build  the  comb  outward.  But  without  this 
assistance  from  man  the  comb  cells  are  usually  remarkably  regular 

and  show  the  greatest 
economy  in  the  use  of 
wax.  The  cross  section 
of  each  cell  is  a  hexagon, 
and  so  these  compart- 
ments fit  together  with- 
out any  spaces  between 
them  as  would  occur  if 
the  cells  were  cylinders. 
(See  Fig.  27.)  This  hex- 
agonal shape  also  permits 
a  single  partition  wall  to 
serve  for  two  adjacent 
cells,  and  it  is  evident 
that  this  shape  of  cell 
more  closely  fits  the  body 
of  the  bee  than  would 
a  four-sided  cell.  The 
worker  bees  build  two 
different  sizes  of  cells  in 
the  comb.  Most  of  the 
cells  average  about 
twenty-five  to  a  square 
inch,  and  in  these  the  fertilized  eggs  are  laid,  which,  as  we  have 
said,  develop  into  workers.  The  cells  in  which  unfertilized  eggs 
are  deposited  are  somewhat  larger.  These  form  the  so-called 
drone  comb. 

The  wax  from  which  the  comb  is  produced  oozes  out  from  cer- 
tain glands  on  the  ventral  surface  of  the  abdomen  of  the  workers. 
When  producing  the  wax  the  bees  hang  motionless  inside  the  hive 
for  several  days,  each  holding  to  the  bees  above.  They  have  al- 


FIG.  27.  —  Worker  cells  and  queen  cells. 
(From  "  A,  B,  C  of  Bee  Culture."  A.  I.  and 
E.  R.  Root.) 


INSECTS 


39 


ready  gorged  themselves  with  honey,  and  it  is  estimated  that  from 
seven  to  fifteen  pounds  of  honey  are  required  to  produce  one  pound 
of  wax.  As  the  little  plates  of  wax  are  formed,  they  are  seized  by  a 
bee  and  carried  with  its  mandibles  or  under  its  "  chin  "  to  the  comb 
where  the  building  is  going  on.  Here  the  wax  is  pressed  against  one 
of  the  walls. 


- -honey 
stomach 


air  sac  -  -  _ 


30.    Honey  making.  —  While  studying  flowers  we  learned  that 

they  secrete  a  sweet  liquid  known  as  nectar.     It  is  this  that  the 

workers  use  for1  honey 

manufacture.    The  bee 

inserts  into  the  blossom 

its  sucking  tongue  and 

pumps   up   the  nectar 

into  a  sac  known  as  the 

honey  stomach  (Fig.  28). 

Here  a  kind  of  digestion 

takes  place  whereby  the 

nectar   is    changed    to 

honey.     If  the  worker 

bee  is  hungry,  it  opens 

a   little   trapdoor   and 

allows  the  honey  and    ing  pore 

pollen  to  pass  into  the 

true     stomach.       But 
since  the  insect  usually 

makes  more  honey  than 
it  can  use,  when  it  re- 
turns to  the  hive  it  squeezes  its  tiny  honey  stomach  and 
deposits  the  surplus  in  the  cells  of  the  comb.  This  honey,  when 
first  made,  contains  a  good  deal  of  water;  it  would  there- 
fore take  up  too  much  room  in  the  comb  and  it  would  be 
more  likely  to  run  out  from  the  horizontal  cells.  Hence,  some 
of  the  workers  fan  with  their  wings  and  evaporate  the  surplus 
water.  When  the  cells  are  completely  filled,  they  are  capped 
over  with  wax. 


FIG.  28.  —  Internal  organs  of  bee.     (Lang.) 


40 


ANIMAL  BIOLOGY 


31.  Other  duties  of  worker  bees.  —  Bees,  we  have  also  learned 
(28),  bring  in  large  quantities  of  pollen  packed  in  the  pollen  baskets 
of  the  hind  legs,  and  in  gathering  pollen  a  considerable  amount 
clings  to  the  head  and  other  parts  of  the  body.     Worker  bees  also 
bring  in  from  the  buds  of  trees  a  brown,  gummy  substance  called 
bee  glue  or  propolis  which  they  use  to  close  up  crevices  in  the  inside 
of  the  hive.     In  most  hives,  too,  certain  bees  seem  to  be  detailed 
to  act  as  soldiers  to  keep  out  individuals  from  another  swarm  or 
other  marauders  which  might  raid  their  stores  of  food.     During  the 
busy  summer  season  a  worker  usually  lives  only  a  month  or  two. 

Certainly  enough  has  been  said  to  convince  any  one  that  a  bee 
colony  is  a  wonderful  social  community,  organized  more  com- 
pletely, so  far  as  division  of  labor  is  concerned,  than  many  a  human 
community.  Is  it  a  monarchy  ruled  by  the  queen,  or  a  democracy 
controlled  by  the  workers?  The  latter  is  more  probably  the  case. 
Yet  we  can  hardly  imagine  how  the  thousands  of  individuals  can 
work  together  in  such  a  helter-skelter  way  and  accomplish  such 
wondrous  results.1 

32.  Life  history  of  the  honeybee.  —  The  eggs  of  the  bee 
are  tiny  white  objects,  shaped  more  or  less  like  a  banana. 
A  single  egg  is  fastened  by  the  queen  mother  at  the  bottom 

of  each  cell  in  the 

young  larva  just  hatched  from  egg 


larva 


pupa 


FIG.  29.  —  Stages  in  life  history  of  honeybee. 

(Cheshire). 


brQ()d 

29).  At  the  end  of 
three  days  the  egg 
hatches  into  a  mi- 
nute footless  grub  or 
larva  (Fig.  29)  which 
is  fed  for  the  first 
few  days  on  rich 

f  ood>     produced     in 

the  stomach  of  the 


1  For  interesting  descriptions  of  the  work  carried  on  in  a  beehive 
see  "A,  B,  C  of  Bee  Culture,"  by  A.  I.  and  E.  R.  Root. 


INSECTS  41 

workers  that  are  acting  as  nurses.  The  grubs  are  then 
fed  with  a  mixture  of  pollen  and  honey,  and  at  the  end  of 
six  days  after  hatching  they  are  supplied  with  enough  of 
this  mixture  to  last  during  the  rest  of  the  larva  stage,  and 
the  cells  are  then  capped  over  with  wax  by  the  workers. 
There  the  developing  bees  pass  through  the  third  or  pupa 
stage  (Fig.  29),  and  at  the  end  of  twelve  days  bite  their 
way  out  of  their  nursery  cells  and  take  their  share  in  the 
busy  toil  of  the  hive. 

Drones,  we  have  said,  develop  in  somewhat  larger  cells 
than  worker  bees.  When  the  colony  wishes  to  produce  a 
queen,  the  workers  build  a  cell  about  as  large  as  the  end- 
joint  of  one's  little  finger  (Fig.  27),  and  as  soon  as  the  egg  is 
hatched  they  stuff  the  little  grub  throughout  the  larval 
stage  with  what  is  called  "  royal  jelly,"  never  giving  it  the 
undigested  pollen  mixture  that  is  supplied  to  the  grubs  of 
workers  or  drones. 


33.  Swarming.  —  We  come  now  to  one  of  the  most  interesting 
events  in  the  story  of  bee  colonies.  If  several  queens  emerge  from 
their  cells  at  the  same  time,  they  attack  each  other  in  a  royal  battle, 
for  it  is  said  that  a  queen  never  uses  her  sting  except  against  a  rival. 
When  the  conflict  is  over,  the  victorious  queen  becomes  the  mother 
of  the  hive.  For  in  the  meantime  the  former  queen,  surrounded  by 
half  the  drones  and  workers,  has  left  the  old  hive,  abdicating  in  her 
daughter's  favor.  After  emerging  from  their  old  home,  the  swarm 
of  bees  thus  formed  alights  on  a  neighboring  tree,  clinging  to  each 
other  in  a  solid  mass.  It  is  then  comparatively  easy  for  a  beekeeper 
to  shake  the  insects  from  the  limb  into  a  new  hive,  and  if  the  queen 
is  secured,  the  swarm  will  usually  begin  work  at  once  in  their  new 
home  (Fig.  30) .  If,  however,  the  bees  are  not  captured,  scouts  go 
out  to  search  for  a  hollow  tree ;  and  when  satisfactory  quarters  are 
found,  the  whole  swarm  follows  their  guides,  and  build  their  comb 
in  the  home  thus  secured. 


42 


ANIMAL   BIOLOGY 


34.  Economic  importance  of  bees.  —  In  our  study  of 
flowers  we  referred  frequently  to  the  necessity  of  the  visits 
of  bees  to  insure  cross-pollination.  Indeed,  Professor  Hodge 
says  ("  Nature  Study  and  Life  ")  that  for  all  practical  purposes 


FIG.  30.  —  A  swarm  of  bees  on  a  limb.     (Lyons.) 

so  far  as  man  is  concerned,  the  honeybee  is  sufficient  for 
this  purpose  (with  the  exception  of  securing  a  red  clover 
crop,  which  requires  the  help  of  the  bumblebee).  In  years 
to  come  we  may  be  sure  that  the  most  successful  fruit  farmers 
Will  also  keep  bees. 

It  is  estimated  that  the  annual  production  of  honey  and 
wax  in  the  United  States  amounts  to  between  twenty  and 
thirty  millions  of  dollars,  and  if  scientific  management  were 
to  be  introduced  more  widely,  this  output  could  be  raised  to 
fifty  million  dollars  a  year  without  additional  investment. 
Almost  any  one  who  is  interested  can  keep  bees.  During  a 


INSECTS  43 

single  season  the  swarm  in  the  observation  hive  on  the  fourth 
floor  of  the  Morris  High  School  in  New  York  City  produced 
fifty-six  pounds  of  honey  in  the  super  boxes,  besides  laying 
by  in  the  brood  chamber  a  sufficient  supply  for  their  winter 
support. 

35.  Relatives  of  the  bees.  —  Wasps  and  hornets  belong  to  the 
same  order  of  insects  as  the  bees,  and  resemble  them  more  or  less 
closely  in  structure.  Some  kinds  of  wasps  build  paper  comb  from 
wood  which  they  chew  up  with  their  jaws.  Ants,  insects  with  which 
every  one  is  familiar,  are  likewise  classed  with  the  bees  and  wasps, 
,and  the  social  communities  that  they  form  are  marvelous  in  the 
degree  to  which  they  carry  division  of  labor.  In  some  ant  colonies 
in  addition  to  the  workers  there  are  soldiers  and  slaves. 

IV.  MOSQUITOES  AND  FLIES 

36.  Life  history  of  the  common  inland  or  house  mosquito. 
—  The  eggs  of  the  common  house  mosquito  are  laid  by  the 
female  in  little  rafts  that  float  on  the  surface  of  stagnant 
water.  These  egg  masses  look  like  flecks  of  black  soot,  but 
when  examined  with  a  hand  lens  each  is  found  to  consist 
of  200  to  400  cartridge-shaped  eggs  standing  on  end  (Fig. 
31).  If  the  weather  is  warm  and  other  conditions  are  favor- 
able, the  eggs  hatch  within  a  day  into  tiny  mosquito  larvae, 
which  are  known  as  "  wrigglers  "  from  their  characteristic 
motion  in  the  water. 

In  the  second  stage  in  its  life  history,  which  usually  lasts 
about  a  week,  the  mosquito  larva  feeds  on  the  microscopic 
plants  and  animals  that  abound  in  all  stagnant  water,  and 
grows  rapidly.  Just  as  was  the  case  with  the  butterfly  and 
moth  caterpillars,  this  rapid  growth  necessitates  the  frequent 
shedding  or  molting  of  the  outer  covering  of  the  larva  and 
the  formation  of  a  new  and  larger  coat.  Hence,  in  water 


44 


ANIMAL  BIOLOGY 


FIG.   31.  —  Life  history  of  house  FIG.  32.  —  Life  history  of  malaria 

mosquito  (Culex).  mosquito  (Anopheles). 

(Howard,  U.  S.  Dept.  of  Agriculture.) 


INSECTS  45 

where  mosquitoes  breed,  one  finds  countless  "  suits  of 
cast-off  clothing  "  which  would  fit  all  stages  of  the  young 
wrigglers. 

The  mosquito  larva  has  a  well-developed  head,  a  thorax, 
and  a  jointed  or  segmented  abdomen,  but  legs  and  wings 
are  wanting.  The  most  striking  characteristic  of  this  stage 
of  the  mosquito  is  the  breathing  tube  that  projects  diag- 
onally from  the  hind  end  of  the  abdomen.  For  while  the 
mosquito  larva  lives  in  the  water,  it  is  obliged  to  swim  to  the 
surface  at  short  intervals  to  get  its  necessary  supply  of  air. 
It  then  hangs  diagonally  with  the  tip  of  its  breathing  tube  pro- 
jecting through  the  surface  film  into  the  air  above  (Fig.  31). 
This  habit  frequently  proves  its  undoing,  as  we  shall  see 
when  we  come  to  discuss  the  methods  of  mosquito  extermi- 
nation. 

After  attaining  its  full  growth  as  a  larva,  the  insect  enters 
the  third  or  pupa  stage  (Fig.  31).  "  The  pupa,"  says  Miss 
Mitchell  in  her  "  Mosquito  Life,"  "  is  the  form  intermediate 
between  the  larva  and  the  adult.  Unlike  most  pupae,  those 
of  the  mosquito  are  very  active,  but  like  other  pupae,  they 
do  not  eat.  They  are  about  the  shape  of  fat  commas, 
floating  quietly  at  the  surface  or  bobbing  crazily  downward 
at  the  least  alarm  to  hide  at  the  bottom,  propelled  by  back- 
ward flips  of  the  abdomen.  .  .  .  The  creature  no  longer 
breathes  through  a  single  tube  on  the  eighth  segment  of  the 
abdomen  but  by  means  of  a  pair  of  tubes  on  the  back  of 
the  thorax."  During  this  stage  the  insect  develops  its 
sucking  mouth  parts,  its  long,  slender  legs,  and  its  two  deli- 
cate wings,  and  all  these  organs  may  be  seen  through  the 
transparent  outer  coat,  which  is  composed  of  a  substance 
known  as  chitin. 

At  the  final  molt  the  mosquito  leaves  its  pupal  case  in  the 
water  and  flies  into  the  air,  an  adult  mosquito.  If  it  hatches 


46  ANIMAL  BIOLOGY 

during  the  spring,  summer,  or  early  autumn,  it  usually 
lives  no  more  than  a  week  or  two ;  but  many  of  the  female 
mosquitoes  that  develop  late  in  the  autumn  seek  out  a 
protected  spot  in  which  to  spend  the  winter,  and  thus  are 
ready  in  the  spring  to  perpetuate  the  species  by  laying 
eggs  in  the  stagnant  pools  formed  by  early  rains. 

All  that  the  mosquito  needs,  therefore,  in  order  to  develop 
its  offspring  from  egg  to  adult  stage  is  a  bit  of  water  that  will 
remain  relatively  undisturbed  for  about  two  weeks.  Hence, 
old  tomato  cans,  bits  of  crockery,  and  other  receptacles 
carelessly  left  in  many  a  back  yard,  furnish  breeding  places 
for  all  kinds  of  mosquitoes. 

Truth  compels  us  to  remark,  in  passing,  that  the  male 
mosquito  is  a  decent  sort  of  fellow,  keeping  close  to  his  breed- 
ing place  and  feeding  on  plant  juices  or  eating  nothing  at 
all  during  his  brief  existence  in  the  adult  stage.  It  is  the 
lady  mosquito  that  torments  us  by  singing  her  piercing  song 
and  piercing  our  suffering  skins.  But  as  in  most  other  suffer- 
ings that  we  endure,  the  fault  is  largely  our  own.  At  least 
we  can  secure  immunity  if  as  communities  we  but  persist 
in  applying  the  simple  methods  of  extermination  outlined 
in  42. 

37.    Life   history   of   malaria-transmitting     mosquitoes. — 

The  mosquito  we  have  just  described,  while  a  nuisance 
wherever  found,  does  not,  so  far  as  is  known,  cause  disease. 
There  are,  however,  two  kinds  of  mosquitoes  that  are  not 
only  a  nuisance  but  a  menace  to  life  and  health  wherever 
they  are  found ;  namely,  those  that  transmit  malaria  and 
yellow  fever.  The  first  of  these  is  the  Anopheles  mosquito, 
commonly  known  as  the  "  malaria  mosquito,"  for  as  we  shall 
soon  see,  malaria  cannot  be  transmitted  from  one  human 
being  to  another  except  through  the  agency  of  this  species 


INSECTS  47 

of  insect.  The  eggs  of  the  Anopheles  mosquito  are  larger 
than  those  of  the  house  mosquito  and  are  laid  singly,  not  in 
masses  (Fig.  32).  In  the  larva  stage,  likewise,  the  two 
insects  may  be  easily  distinguished  from  the  fact  that  the 
"  malaria  wriggler,"  while  breathing,  lies  horizontally  just 
beneath  the  surface  of  the  water,  while  the  other  species 
hangs  downward,  with  only  the  tip  of  the  breathing  tube 
projecting  to  the  water  level  (Figs.  31  and  32). 

In  Figs.  31  and  32  the  characteristic  position  of  the  adults 
of  the  two  species  is  shown.  While  the  body  of  the  house 
mosquito  is  usually  parallel  to  the  surface  on  which  it  alights, 
that  of  the  malaria-transmitting  insect  is  sharply  tilted  away 
from  the  surface. 

38.  Occurrence  of  malaria.  —  The  story  of  the  discovery 
that  a  kind  of  mosquito  known  as  the  Anopheles  mosquito  is 
the  only  means,  as  far  as  we  now  know,  by  which  malaria 
may  be  transmitted  from  one  individual  to  another,  is  one  of 
the  most  wonderful  in  all  the  history  of  biology.  In  a  guide 
leaflet  on  "  The  Malaria  Mosquito  "  published  by  the  Ameri- 
can Museum  of  Natural  History,  New  York  City,1  the 
author,  B.  E.  Dahlgren,  writes  as  follows :  — 

"  It  was  early  observed  that  'malaria'  was  apt  to  be  prev- 
alent during  the  damp  and  rainy  seasons,  and  that  it  oc- 
curred principally  in  exactly  such  places  as  are  now  known 
to  furnish  ideal  breeding  grounds  for  the  malaria  mosquito. 
That  new  cases  of  malaria  appeared  at  the  time  of  year  when 
the  Malaria  Mosquito  abounded,  was  also  recorded  long 
before  it  was  suspected  that  the  insect  was  in  any  way  con- 

1  Every  one  who  visits  the  American  Museum  should  study  care- 
fully the  wonderful  set  of  models  that  show  on  a  big  scale  the 
various  stages  in  the  life  history  of  the  mosquito.  These  models 
are  pictured  in  the  bulletin  referred  to  above,  which  may  be  ob- 
tained from  the  librarian  of  the  Museum  for  fifteen  cents. 


48  ANIMAL   BIOLOGY 

nected  with  the  malady ;  and  one  of  the  old  medical  writers 
mentions  as  a  characteristic  of  malaria  seasons  that  'gnats 
and  flies  are  apt  to  be  abundant.'  .  .  . 

"  Malaria  was  formerly  considered  to  be  a  form  of  ague 
due  to  foul  air,  whence  its  name,  which  literally  means  '  bad 
air.'  It  was  attributed  to  a  sort  of  '  miasma.'  Its  true 
nature  did  not  become  known  till  1880,  when  Laveran,  a 
French  military  surgeon,  working,  at  the  time,  in  Algeria, 
discovered  the  malarial  parasite  in  human  blood."  Major 
Ross,  an  English  officer  in  India,  later  proved  the  presence 
of  the  parasite  in  the  body  of  the  mosquito. 

39.  Transmission  of  malaria.  —  Investigation  has  shown 
that  the  parts  of  the  world  where  Anopheles  abound  are  the 
eastern  half  of  the  United  States  and  a  large  part  of  Europe, 
together  with  many  regions  of  the  tropics.  It  is  a  well- 
known  fact  that  these  are  the  regions,  too,  in  which  malaria 
is  very  abundant,  and  this  is  the  first  line  of  proof  that  the 
Anopheles  mosquito  is  always  responsible  for  the  trans- 
mission of  malaria. 

Even  more  conclusive  were  the  experiments  of  four  investi- 
gators who  spent  the  fever  season  in  the  dreaded  malaria 
district  of  the  Roman  Campagna.  They  built  for  themselves 
a  carefully  screened  house  in  which  they  remained  from  sun- 
set to  sunrise,  and  this  was  the  only  precaution  that  they  ob- 
served. In  the  daytime  they  went  freely  among  those  who 
were  stricken  with  the  fever,  they  allowed  themselves  to  be 
soaked  with  the  falling  rains,  and  at  night  the  air  from  the 
swamps  came  freely  into  their  sleeping  quarters.  But  while 
hundreds  of  malaria  cases  were  all  about  them,  not  one  of  the 
four  contracted  the  disease.  Hence,  to  escape  malaria,  one 
has  only  to  make  sure  that  Mrs.  Anopheles  is  prevented  from 
injecting  her  billful  of  malaria  germs  —  and  this  she  does 


INSECTS  49 

only  during  night  time,  "  loving  darkness,  rather  than  light, 
because  her  deeds  are  evil." 

In  the  year  1890  Dr.  Manson  and  Dr.  Warren,  two  physi- 
cians in  London,  allowed  themselves  to  be  bitten  by  Ano- 
pheles mosquitoes  that  had  previously  bitten  malaria  pa- 
tients in  Italy.  In  eighteen  days  both  developed  malarial 
fever  and  in  the  blood  of  both,  malaria  organisms  were  found, 
although  previous  to  this  infection  from  the  mosquito 
neither  had  suffered  in  any  way  from  the  disease. 

40.  Life  history  of  the  malaria  parasite.  —  But  yet  more  wonder- 
ful proof  that  the  mosquito  transmits  malaria  has  been  furnished 
by  the  microscopes  of  biologists.  The  discovery  of  the  malarial 
parasite  by  Laveran  in  1880  has  already  been  referred  to.  This 
resembles  in  its  form  and  activities  a  single-celled  animal  known  as 
the  Amoeba  (124).  When  this  organism  of  malaria  is  present  in 
human  blood,  it  bores  its  way  into  a  red  corpuscle  (H.  B.,  6),  feeds 
upon  the  contents  of  this  blood  cell,  and  grows  at  the  expense  of  the 
corpuscle  until  the  parasite  occupies  nearly  all  the  space  inside  it 
(Fig.  33).  The  malaria  parasite  then  divides  into  a  number  (6-16) 
of  daughter  parasites,  which  rupture  the  red  corpuscle  in  which  they 
have  been  developing,  and  escape  into  the  liquid  part  of  the  blood, 
thus  causing  the  chills  so  characteristic  of  malaria.  Each  new  para- 
site then  attacks  a  new  corpuscle  and  at  the  end  of  two  or  three  days 
produces  six  to  sixteen  new  spores,  and  so  the  organisms  multiply. 

Now  here  comes  the  relation  of  the  mosquito  to  malaria.  For 
when  the  female  Anopheles  bites  a  person  having  malaria,  she  is 
likely  to  suck  up  blood  that  contains  malaria  organisms  in  a  cer- 
tain stage  of  development.  These  reach  the  insect's  stomach,  where 
they  pass  through  a  stage  known  as  fertilization.  In  the  stomach  of 
a  single  mosquito  as  many  as  five  hundred  of  these  fertilized  cells 
have  been  counted.  Each  cell  then  becomes  pointed  at  one  end, 
bores  its  way  through  the  wall  of  the  mosquito's  stomach,  and  in 
fifteen  to  twenty  days  produces  relatively  large  swellings  on  the 
outer  surface,  in  which  are  thousands  of  needle-shaped  malaria 
spores  (Fig.  33). 
E 


50 


ANIMAL  BIOLOGY 


At  length  these  spores  escape  through  the  outer  wall  of  the 
mosquito's  stomach  and  many  of  them  find  their  way  to  the  salivary 
glands.  And  so  when  the  infected  mosquito  bites  another  person, 
these  parasites  are  injected  with  the  saliva,  and  if  the  conditions  are 
favorable  in  the  blood  of  the  new  victim,  the  spores  straightway 
attack  the  red  corpuscles,  and  a  new  case  of  malaria  is  the  result. 

For  the  treatment  of  malaria  quinine  is  the  most  effective  drug 
known  at  present.  It  should  be  taken  in  the  quantity  and  at  the 
times  prescribed  by  the  physician. 


malaria  parasite  enter- 
ing a  red  blood  cor- 
puscle and  develop- 
ing 13  new  parasites 


stomach  of  a  mosquito 
with  swellings  filled 
with  malaria  spores 


!  malaria  spores  from 
salivary  glands  of 
mosquito  (much  en- 
larged) 

FIG.   33.  —  Life  history  of  the  malaria  parasite.     (Dahlgren,  American 
Museum  Natural  History.) 

41.  Transmission  of  yellow  fever.  —  The  proof  that  malaria  can 
only  be  transmitted  from  one  human  being  to  another  was  largely 
the  work  of  the  biologists  of  England,  France,  and  Italy.  The  dis- 
covery that  another  kind  of  mosquito  (Stegomyia)  is  responsible  for 
the  transmission  of  the  parasite  that  causes  yellow  fever  is  due  al- 
most wholly  to  the  splendid  achievements  of  the  Yellow  Fever  Com- 
mission appointed  by  President  McKinley.  In  June,  1900,  this 
commission  of  five,  headed  by  Dr.  Walter  Reed  (Fig.  34),  began  its 
epoch-making  experiments  in  the  Island  of  Cuba,  and  within  six 


INSECTS  51 

months  these  men  demonstrated  conclusively  that  this  plague 
disease  of  the  tropics  and  of  our  southern  states  can,  so  far  as  we 
know,  be  communicated  only  through  the  agency  of  the  Stegomyia 
mosquito. 

This  commission,  believing  in  the  mosquito  theory,  at  once  began 
experiments  to  demonstrate  its  truth.     One  of  the  members,  Dr. 


FIG.  34.  — Dr.  Walter  Reed. 


Lazear  (Fig.  35),  permitted  a  mosquito  to  bite  him ;  a  few  days  later 
he  contracted  the  disease  and  died.  The  inscription  on  a  tablet 
erected  in  his  memory  reads  as  follows :  "  With  more  than  the 
courage  and  devotion  of  the  soldier,  he  risked  and  lost  his  life  to 


52 


ANIMAL  BIOLOGY 


show  how  a  fearful  pestilence  is  communicated  and  how  its  ravages 
may  be  prevented." 

When  Dr.  Reed  called  for  volunteers  from  among  the  soldiers,  the 
first  to  respond  "  was  a  young  private  from  Ohio,  named  John  R. 


FIG.  35.  —  Dr.  Jesse  Lazear. 

Kissinger  (Fig.  36),  who  volunteered  for  the  service,  to  use  his  own 
words,  '  solely  in  the  interest  of  humanity  and  the  cause  of  science/ 
When  it  became  known  among  the  troops  that  subjects  were  needed 
for  experimental  purposes,  Kissinger,  in  company  with  another 
young  private  named  John  J.  Moran,  also  from  Ohio,  volunteered 
their  services.  Dr.  Reed  talked  the  matter  over  with  them,  ex- 


INSECTS 


53 


plaining  fully  the  danger  and  suffering  involved  in  the  experiment 
should  it  be  successful,  and  then,  seeing  they-  were  determined,  he 
stated  that  a  definite  money  compensation  would  be  made  them. 
Both  young  men  declined  to  accept  it,  making  it,  indeed,  their  sole 
stipulation  that  they  should  receive  no  pecuniary  reward,  where- 
upon Major  Reed  touched  his  cap,  saying  respectfully,  'Gentlemen, 
I  salute  you.'  Reed's  own  words  in  his  published  account  of  the 
experiment  on  Kissinger  are :  '  In  my  opinion  this  exhibition  of 
moral  courage  has  never  been 
surpassed  in  the  annals  of  the 
Army  of  the  United  States.'  "  l 

The  object  of  one  of  the  first 
experiments  was  to  determine 
whether  or  not  yellow  fever  could 
be  contracted  from  clothing  worn 
by  yellow  fever  patients.  A  small 
building  was  constructed  the  win- 
dows and  doors  of  which  were 
carefully  screened.  Into  this 
were  brought  chests  of  clothing 
that  had  been  taken  from  the 
beds  of  patients  who  had  been 
sick  and  in  some  cases  had  died 
of  yellow  fever.  Three  brave 
men  entered  the  building,  un- 
packed the  boxes,  and  for  twenty 
nights  slept  in  close  contact  with 
the  soiled  clothing.  "  To  pass 
twenty  nights  in  a  small,  ill- ventilated  room,  with  a  temperature 
over  ninety,  in  close  contact  with  the  most  loathsome  articles 
of  dress  and  furniture,  in  an  atmosphere  fetid  from  their  presence, 
is  an  act  of  heroism  which  ought  to  command  our  highest  ad- 
miration and  our  lasting  gratitude."2  In  spite,  however,  of  their 
unwholesome  surroundings,  none  of  the  men  contracted  yellow 


FIG.  36.  —  John  R.  Kissinger,  U.S.A. 


"Walter  Reed  and  Yellow  Fever,"  by  Dr.  H.  A.  Kelly 
Doubleday,  Page  &  Co.  2  "Walter  Reed  and  Yellow  Fever." 


54 


ANIMAL  BIOLOGY 


fever,  and  so  it  was  proved  for  all  time  that  this  disease  cannot  be 
communicated  by  means  of  anything  that  conies  from  the  body 
of  yellow  fever  patients. 

Dr.  Reed  now  sought  to  prove  that  the  Stegomyia  mosquito  was 
the  means  by  which  the  disease  was  transmitted  from  one  person  to 
another.  A  second  building,  the  same  size  as  the  first,  was  erected, 
the  room  was  divided  by  a  wire  screen,  and  all  the  doors  and  windows 
were  carefully  screened  (Fig.  37) .  Into  one  of  the  rooms  a  number  of 
mosquitoes  that  had  bitten  yellow  fever  patients  were  freed  and  a 


(3U 
\ 


te>~Ki 

-  1    <&we 


FIG.   37.  —  Plan  of  infected  mosquito  building, 
by  John   R.  Kissinger.) 


(Drawn  for  the  authors 


few  minutes  later  John  Moran,  an  Ohio  soldier,  entered  and  allowed 
these  mosquitoes  to  bite  him.  "  On  Christmas  morning  (1900)  at 
11  A.M.  this  brave  lad  was  stricken  with  yellow  fever  and  had  a 
sharp  attack  which  he  bore  without  a  murmur."  On  the  other  side 
of  the  screen  were  three  soldiers  who  were  protected  from  mos- 
quitoes ;  and  these  men  remained  in  perfect  health.  This  experi- 
ment proved  conclusively  that  yellow  fever  is  transmitted  by  the 
Stegomyia  mosquito. 

42.    Extermination  of  mosquitoes.  —  Now  all  the  suffer- 
ing from  malaria  and  yellow  fever  is  entirely  unnecessary 


INSECTS  55 

if  communities  will  but  take  the  trouble  to  eradicate  all 
breeding  places  of  mosquitoes.  Since  the  mosquito,  during 
its  development  in  the  water,  comes  frequently  to  the  surface 
to  secure  air  for  breathing,  a  thin  film  of  oil  spread  over  the 
surface  of  the  water  in  which  they  are  breeding  is  a  sure 
means  of  killing  them.  But  the  kerosene  treatment  is  at 
best  but  a  temporary  means  of  ridding  a  community  of  mos- 


FIG.  38.  —  Staten  Island  marshes  before  drainage. 

quitoes.  The  oil  has  to  be  renewed  every  two  or  three  weeks, 
especially  after  rains,  to  make  sure  that  a  continuous  film 
covers  the  surface.  Hence,  wherever  possible,  pools  should 
be  drained,  and  one  has  but  to  read  Dr.  Doty's  account  of 
his  marvelous  success  in  abating  the  mosquito  nuisance  on 
Staten  Island  (see  New  York  State  Journal  of  Medicine, 
May,  1908)  to  be  convinced  that  this  method  is  effective 
(Figs.  38  and  39).  Every  householder  should  cooperate  by 


56  ANIMAL  BIOLOGY 

cleaning  up  his  own  back  yard  and  by  covering  cisterns 
and  wells  with  the  finest  meshed  netting ;  for  the  insistent 
mosquito  has  been  known  to  make  its  way  through  ordinary 
wire  netting.  Fish  and  dragon  flies  are  also  important 
helps  to  man,  since  these  animals  devour  great  numbers 
of  larvae,  pupae,  and  adult  insects;  yet  at  best  they  can 
hardly  be  counted  as  efficient  means  of  ridding  swamps  of 
mosquito  pests. 

Anopheles,  Culex,  and  Stegomyia  lay  their  eggs  in  the  same 


FIG.  39.  — Staten  Island  marshes  after  drainage. 

kind  of  stagnant  pools,  and  the  proper  filling,  draining,  or 
screening  of  these  pools  or  their  treatment  with  kerosene, 
will  destroy  the  one  as  well  as  the  other.  When  this  is  ac- 
complished, malaria  and  yellow  fever,  as  has  been  con- 
clusively demonstrated  by  the  work  of  Americans  on  Staten 
Island,  New  Orleans,  Cuba,  and  Panama,  will  practically 
disappear. 


INSECTS  57 

43.  Habits    and   life    history    of  the  house  fly.  —  It  has 
been  clearly  proved  that  the  common  house  fly  is  a  fre- 
quent cause  of  disease;   especially  is  this  true  in  the  trans- 
mission of  typhoid  fever  and  the  intestinal  diseases  to  which 
the  deaths  of  so  many  young  children  are  due.     Practically 
all  parts  of  the  body  of  a  fly  are  covered  with  hairs  (Fig.  41), 
especially  the  mouth  parts  and  feet.     Each  foot,  also,  has 
sticky  pads  (Fig.  40)  which  enable  the  fly  to  cling  to  the  walls 
and  ceilings.     In  the  adult  stage  the  flies  feed  upon  filth 
of  all  sorts,  and  if  they  alight  on  the  excretions  of  typhoid 
patients,  they  are  very  likely  to  carry  on  their  feet  and 
mouth  parts  the  germs  of  the  disease,  and 

so  when  they  come  into  the  house,  they 
may  infect  milk  and  other  food.  Flies 
also  carry  germs  of  other  diseases  such  as 
cholera,  dysentery,  and  tuberculosis. 

The  most  common  breeding  place  of  FIG.  40.  — Foot  of  fly, 
house  flies  is  in  piles  of  horse  manure.  ^ing  hairs  and 
Here  the  female  fly  lays  about  120  eggs 
(Fig.  41)  which  hatch  within  a  few  hours  into  tiny  white 
footless  grubs.  These  feed  for  about  five  days  upon  the 
manure  and  grow  rapidly,  molting  twice  within  that  time. 
The  larva  now  changes  into  a  pupa,  and  at  the  end  of  another 
five  days  the  adult  fly  emerges  from  the  brown  pupa  case. 
Egg  laying  begins  almost  at  once,  and  as  each  adult  female 
fly  lays  120  eggs,  it  has  been  estimated  that  a  single  fly  may 
have  5,598,720,000  descendants  in  a  single  season  if  each  fly 
were  to  deposit  but  one  batch  of  eggs.  In  reality,  however, 
a  fly  deposits  four  batches  in  a  season.  Hence  it  is  very  impor- 
tant to  catch  and  kill  flies  at  the  very  beginning  of  each  season. 

44.  Extermination  of  house  fly.  —  Because  of  the  danger 
of  disease  transmission  every  housekeeper  should  do  her  best 


58 


ANIMAL  BIOLOGY 


to  screen  her  house  and  so  keep  flies  away  from  food,  for  one 
never  knows  where  these  insects  have  been  crawling  or  what 
disease  germs  may  be  clinging  to  their  feet.  City  authorities 


eggs  larva  pupa  adult 

FIG.  41.  —  Life  history  of  house  fly. 

should  see  that  all  street  refuse  and  garbage  are  removed  be- 
fore flies  of  any  kind  can  lay  their  eggs  therein.     All  persons 


FIG.  42. —  Life  history  of  potato  beetle.     Identify  eggs,  larvae,  pupa 
and  adult. 


INSECTS 


59 


responsible  for  horse  stables  should  make  sure  that  the 
manure  is  thrown  into  screened  pits  and  sprinkled  with 
chloride  of  lime  at  least  once  a  week. 

Another  method  of  dealing  with  the  problem  is  that  sug- 
gested by  Professor  C.  J.  Hodge  of  Clark  University,  Worces- 
ter, Mass.  It  is  that  of  letting  the  flies  catch  themselves. 
He  has  devised  a  simple  and  inexpensive  flytrap,  which  is 
easily  attached  to  any  garbage  can  (or  to  a  window  screen)  ; 
or  it  may  be  baited  with  bits  of  fish  or  other  food.  The 
flies  are  attracted  by  the  odors  of  the  garbage  or  food  bait, 
and  when  caught  may  be  killed  with  boiling  water.  If  the 
various  suggestions  are  followed,  even  farmhouses,  as  ex- 
perience has  shown,  may  be  rendered  practically  free  from 
the  filthy  and  dangerous  house  fly. 


V.   ADDITIONAL  TOPICS  ON  INSECTS 

45.  Field  and  library  study  of  other  insects.  —  (Optional.)  Study 
as  many  of  the  following  insects  as  time  allows,  consulting  Sander- 
son's "Insect  Pests  of  Farm,  Garden,  and  Orchard,"  Hodge's  "Na- 
ture Study  and  Life,"  National  and  State 
Circulars  and  Bulletins,  articles  in  Ency- 
clopedias or  other  reference  books.  Em- 
phasize especially 
the  habits,  life 
history,  and  eco- 
nomic importance 
of  each  of  the  fol- 
lowing insects: 
Colorado  potato 
beetle  (Fig.  42), 
cut  worms,  army 

worms,    San   Jose 

i    /TT     ,io\   x  FIG.  44.  —  A,   human 

scale  (Fig.43),  tent       louse.    B    eggs    at_ 

caterpillar,  chinch        tached  to  hair. 


FIG.  43.  — San  Jose  scale 
insects  on  pear.  Above, 
single  scale  enlarged. 
(Howard.) 


60 


ANIMAL  BIOLOGY 


bug,  cockroaches,  plant  lice,  human  lice 
(Fig.  44),  bedbugs  (Fig.  45),  carpet  beetles, 
lady  bugs,  scavenger  beetles,  ichneumon  fly. 

46.  Annual  loss  due  to  insect  pests  of 
the  United  States.1  —  "  In  no  country  in 
the  world  do  insects  impose  a  heavier  tax  on 
farm  products  than  in  the  United  States. 
The  losses  resulting  from  the  depredations 
of  insects  on  all  the  plant  products  of  the 
soil,  both  in  their  growing  and  in  their  stored  state,  together  with 
depredations  on  live  stock,  exceed  the  entire  expenditures  of  the 
national  government,  including  the  pension  roll  and  the  mainte- 
nance of  the  army  and  the  navy."  This  loss  for  the  year  1904 
was  estimated  at  $795,100,000,  and  this  does  not  include  the 
expense  involved  in  applying  insecticides. 


FIG.  45. —  Bedbug. 


PRODUCT 

VALUE 

PERCENT- 
AGE OF 
Loss 

AMOUNT  OF  Loss 

Cereals      

$2,000,000,000 

10 

$200,000,000 

Hav 

530,000,000 

10 

53,000,000 

Cotton           

600,000,000 

10 

60,000,000 

Tobacco 

53,000,000 

10 

5,300,000 

Truck  crops        .... 

265,000,000 

20 

53,000,000 

Sugar        

50,000,000 

10 

5,000,000 

Fruits 

135,000,000 

20 

27,000,000 

Farm  forests       .... 
Miscellaneous  crops    .     . 
Animal  products     .     .     . 

.  110,000,000 
58,000,000 
1,750,000,000 

10 
10 
10 

11,000,000 
5,800,000 
175,000,000 

Total 

$5,551,000,000 

$595,100,000 

Natural  forests  and  forest 
products     
Products  in  storage     .     . 

100,000,000 
100,000,000 

Grand  total      .     .     . 

$795,100,000 

1  C.  L.  Marlitt  in  Year  Book  of  United  States  Department  of 
Agriculture,  1904.  The  figures  are  regarded  as  conservative  esti- 
mates. 


INSECTS 


61 


47.  Insecticides.1  —  In  our  laboratory  studies  we  have  found  that 
there  are  two  kinds  of  insects,  namely  those  with  biting  mouth  parts 
and  those  with  sucking  mouth  parts.  Entirely  different  treatment 
is  necessary  in  dealing  with  insect  pests  of  these  two  types.  Insects 
with  biting  mouth  parts  may  usually  be  killed  by  thoroughly  spray- 
ing the  parts  of  a  plant  upon  which  they  feed  with  a  mixture  made 
in  the  following  proportions :  — 


1  GAL.  MIXTURE 

50  GAL.  MIXTURE 

Arsenate  of  lead  (poison)  .     . 
Water    

f  oz.  (1  teaspoon- 
ful) 
Igal. 

2£lb. 
50  gal. 

Insects  with  sucking  mouth  parts,  on  the  other  hand,  must  be 
treated  with  a  spraying  mixture  which  will  actually  touch  their 
bodies.  Some  of  the  "  contact  insecticides  "  for  this  purpose  are 
whale  oil  soap  (one  pound  to  five  gallons  of  water),  kerosene  emul- 
sion, and  "  black-leaf-40."  The  last  named  is  preferable  for  killing 
plant  lice  and  it  is  mixed  with  soap  as  follows :  — 


1  GAL.  MIXTURE 

50  GAL.  MIXTURE 

Black-leaf-40     (40   per    cent 
nicotine)      

Ivory  or  laundry  soap  .     .     . 
Water    

i  oz.  (  =  1  spoon- 
ful) 
|  oz.  (size  of  two 
yeast  cakes) 
1  gal 

Jib. 
21b. 
50  gal 

1  The  authors  are  indebted  to  Professor  Glenn  W.  Herrick  of 
Cornell  University  for  these  formulas. 


CHAPTER .  II 
BIRDS 

48.    Study  of  a  bird.  —  (Optional  home  work.) 

So  far  as  possible  the  following  study  should  be  made  from  a  robin, 
sparrow,  chicken,  or  other  living  bird,  and  the  observations  should 
be  supplemented  by  an  examination  of  stuffed  specimens,  charts, 
or  pictures. 

A.  Regions. 

In  all  animals  that  have  internal  bony  skeletons  as  do  birds,  at 
least  two  of  the  following  regions  may  be  distinguished; 
namely,  a  head,  a  neck,  a  trunk,  and  a  tail. 
Which  of  the  four  regions  named  above  can  you  dis- 
tinguish in  the  bird  that  you  are  studying? 

B.  Head. 

1.  Describe  the  general  shape  of  the  beak  (or  bill},  stating 

whether  it  is  relatively  long  and  slender,  or  short  and 
thick.  State,  also,  whether  the  tip  of  the  beak  is  straight 
or  curved.. 

2.  On  what  part  of  the  head  are  the  eyes  located? 

In  the  eyes  of  a  bird  the  following  parts  are  visible  :  a  central 
pupil,  and  around  this  a  colored  region  known  as  the 
iris.  State  the  location  and  describe  the  color  of 
each  of  these  parts  in  the  eye  of  the  bird  that  you  are 
studying. 

3.  In  front  of  the  eyes  find  two  openings,  the  nostrils.     Locate 

the  nostrils  with  reference  to  the  beak  and  the  eyes. 

4.  Make  a  drawing  twice  natural  size  of  a  side  view  of  the  head 

to  show  the  beak,  eye,  and  nostril.  Label  each  part 
shown. 

62 


BIBDS  63 

5.  Watch  a  chicken,  canary,  sparrow,  or  other  bird  while  it  is 
eating  and  drinking,  and  describe  the  movements  that 
the  bird  makes  in  these  acts. 

C.  Organs  of  locomotion. 

1.  What  is  the  position  of  the  wings  when  they  are  not  in  use? 

2.  Note  and  describe  the  movements  of  the  wings  when  the  bird 

is  flying. 

3.  The  only  part  of  the  leg  that  is  visible  in  most  birds  is  the 

foot,  the  upper  parts  being  covered  with  feathers. 

a.  How  many  toes  do  you  find  pointing  forward  and  how 

many  backward?     (Be  sure  to  name  the  kind  of  bird 
on  which  this  observation  is  made.) 

b.  Make  a  drawing  to  show  the  foot  and  the  toes  with  the 

claws  at  the  end  of  each.     Label  toes  and  claws. 

4.  Watch  several  kind  of  birds  (e.g.  robins,  sparrows,  chickens, 

starlings),  and  state  whether  each  of  these  kinds  of 
birds  walks  or  hops. 

49.  What  is  a  bird?  —  Birds,  like  fishes,  frogs,  and  man, 
belong  to  the  group  of  animals  that  have  a  backbone,  and 
hence  are  known  as  vertebrates.  It  is  never  difficult,  however, 
to  distinguish  birds  from  other  vertebrates,  since  every  bird 
has  wings  either  developed  or  undeveloped  (Fig.  46)  and  a 
covering  of  feathers.  Birds,  too,  maintain  a  body  temperature 
that  is  higher  than  that  of  any  other  group  of  animals. 
The  temperature  in  man,  for  instance,  is  normally  about 
98^°  F.,  whereas  no  bird,  so  far  as  we  know,  has  a  tempera- 
ture less  than  100°  F.,  and  even  111°  F.  is  known  to  be 
the  temperature  of  some  of  the  sparrows  and  warblers. 
Hence,  we  may  define  a  bird  as  a  warm-blooded  vertebrate, 
having  wings  and  a  body  covering  of  feathers  and  usually 
able  to  fly. 

Even  a  casual  examination  will  show  that  a  bird  has  a  head, 
neck,  and  trunk,  and  two  pairs  of  appendages,  namely,  the 


64 


ANIMAL  BIOLOGY 


wings  and  legs.     With  the  exception  of  the  feet,  practically 
the  whole  of  the  animal  is  covered  with  feathers  (Fig.  46). 


Scapulars 

"\ftof  &**. 


-Outer] 
FIG.  46.  —  External  structure  of  a  bird. 

50.  Head.  —  A  closer  study  of  a  bird  shows  that  from  the 
front  part  of  the  head  projects  a  horny  structure  known  as 
the  beak  or  bill.  "  Tie  a  man's  hands  and  arms  tightly 
behind  his  back,  stand  him  on  his  feet,  and  tell  him  that  he 
must  hereafter  find  and  prepare  his  food,  build  his  house, 
defend  himself  from  his  enemies  and  perform  all  the  busi- 
ness of  life  in. such  a  position,  and  what  a  pitiable  object  he 
would  present !  Yet  this  is  not  unlike  what  birds  have  to 
do.  Almost  every  form  of  vegetable  and  animal  life  is  used 
as  food  by  one  or  another  of  the  species.  Birds  have  most 
intricately  built  homes,  and  their  methods  of  defense  are  to 
be  numbered  by  the  score ;  the  care  of  their  delicate  plumage 


BIRDS 


65 


alone  would  seem  to  necessitate  many  and  varied  instru- 
ments :  yet  all  this  is  made  possible,  and  chiefly  executed,  by 
one  small  portion  of  the  bird  —  its  bill  or  beak."  1 

While  the  size  and  shape  of  the  bill  varies  greatly  in  differ- 
ent kinds  of  birds,  it  always  consists  of  two  parts  (mandibles) 
(Fig.  46),  which  correspond  in  position  to  the  upper  and 
lower  jaws  of  man.  When 
the  bill  is  opened,  a  careful  ex- 
amination shows  that  a  bird 
has  no  teeth.  Some  of  the 
birds  that  lived  ages  ago, 
however,  had  well-developed 
teeth  in  their  jaws,  as  is  well 
shown  in  (Fig.  47)  which  is  a 
picture  of  a  bird  skeleton  re- 
stored from  bones  found  in 
the  rocks  of  western  Kansas. 

Near  the  base  of  the  bill 
on  either  side,  one  can  usually 
see  an  opening ;  these  open- 
ings are  the  nostrils.  On  the 
sides  of  the  head  are  the  two 
eyes,  and  since  they  bulge  out 
somewhat,  the  bird  is  afforded  a  wide  range  of  vision.  If 
the  feathers  below  and  behind  the  eye  are  pushed  aside,  an 
opening  into  the  ear  may  be  seen ;  this  may  be  made  out  easily 
in  the  head  of  a  chicken. 

51.  Wings.  —  In  Figure  48  are  shown  the  bones  that  com- 
pose the  wing  of  an  ostrich  and  the  arm  of  a  man,  and  on  com- 
paring the  two  one  sees  a  striking  resemblance.  In  both, 
the  upper  arm  has  a  single  bone,  while  in  the  forearm  there 

iBeebe,  "The  Bird." 


FIG.  47.  —  Skeleton  of  a  fossil  bird. 


66 


ANIMAL  BIOLOGY 


are  two  bones.     In  the  hand  region,  though  the  differences 

are  more  striking,  the  general  plan  of  the  two  is  the  same. 

Unlike  the  bones  of  the  human  skeleton  those  of  most  birds 

are  hollow  and  filled  with  air. 

Any  one  who  has  eaten  a  chicken's  wing  knows  that  the 

bones  are  covered  by  muscles ;  these  enable  the  bird  to  fold 

and  unfold  the 
parts  of  the  wing, 
much  as  the  human 
arm  is  stretched  out 
or  doubled  up.  On 
the  bird's  body  are 
other  powerful  mus- 
cles, which  cause 
the  wing  as  a  whole 
to  make  the  upward 
and  downward 
strokes  in  flight. 

Still  another  won- 
derful adaptation  of 
the  wing  for  flight 
is  evident  in  the 
arrangement  and 
structure  of  the 
feathers  (Fig.  49). 
The  feathers  fit  over 
each  other  in  such 


FIG,  48.  —  A,  skeleton  of  arm  of  a  man  ;  B,  skele- 
ton of  wing  of  an  ostrich.      (A.  E.  Rueff.) 


a  way  1  that  in  the  downward  and  backward  stroke  of  the 
wing  a  continuous  surface  is  struck  against  the  air,  and 
this  propels  the  bird  upward  and  forward.  In  the  up- 

1  Before  assigning  these  paragraphs  the  structure  of  a  feather  and 
the  arrangement  of  the  feathers  on  the  wing  of  some  bird  (e.g.  a 
chicken)  should  be  demonstrated  to  the  class. 


BIRDS 


67 


ward  wing  stroke,  on  the  other  hand,  the  resistance  of  the 
air  is  diminished  since  the  feathers  are  separated  more  or 


FIG.  49.  —  Wing  of  Tern.       (Photographed  by  E.  R.  Sanborn,  N.  Y. 
Zoological  Park.) 

less  like  the  slats  of  a  Venetian  blind,  thus  allowing  the  air 
to  pass  between  them. 


shaft 
FIG.  50.  — Structure  of  a  feather. 


barb 


An  examination  of  a  single  feather l  shows  that  it  consists 
in  the  first  place  of  a  shyft  running  through  its  length  (Fig. 
1  See  footnote,  p.  66. 


68 


ANIMAL  BIOLOGY 


50,  A).  On  the  sides  of  the  shaft  are  the  two  flat  surfaces 
which  make  up  the  vane.  This  vane  is  composed  of  slender 
parts  called  barbs  that  may  be  easily  separated  from  each 

other,  or  when  sep- 
arated may  be  read- 
ily united,  because 
of  little  hooks  (Fig. 
50,  B).  This  the 
bird  does  when  it 
smooths  or  "preens" 
its  feathers. 

62.  Legs.— On 
comparing  the  arm  of 
man  with  the  wing  of 
a  bird  we  found  that 
they  were  similar  in 
structure,  and  the 
same  is  likewise  true 
of  the  leg  and  foot. 
While  the  thigh  of  a 
bird  is  much  shorter 
proportionately  than 
is  that  of  man  (Fig. 
51),  both  have  but  a 
single  bone.  Below 
the  knee  of  the  bird 
is  the  shank  or  "drum- 
stick" which  consists 
of  a  long  bone  ex- 
tending to  the  ankle, 
and  beside  it  is  a 
slender  bone  attached  only  at  the  upper  end.  This  region  in  the 
leg  of  man  is  likewise  composed  of  a  relatively  thick  shin  bone,  on 
the  outer  side  of  which  is  a  thin  bone  extending  down  to  the  ankle. 


FIG.  51.  —  A,  skeleton  of  leg  of  an  ostrich;  B, 
skeleton  of  leg  of  a  man.     (E.  R.  Sanborn.) 


BIRDS 


69 


The  ankle  region  of  a  bird  is  the  joint  half-way  up  the  leg  (Fig. 51,  A). 
What  is  commonly  regarded  as  the  bird's  foot  consists  often  of 
three  toes  that  point  forward,  and  one  that  extends  backward. 
Ordinarily  the  parts  of  the  leg  below  the  ankle  are  covered  with 
scales,  and  the  tips  of  the  toes  are  provided  with  claws. 

53.    Study  of  a  hen's  egg.  —  (Optional  home  work.) 
Secure  the  egg  of  a  hen  or  other  domestic  bird,  and  study  it  as 
follows :  — 

1.  Describe  the  difference  in  the  shape  and  size  of  the  two  ends  of 

the  egg. 

2.  Carefully  crack  the  shell  at  the  larger  end  and  remove  the  pieces 

of  shell. 

a.  State  what  you  have  done  and  describe  the  membrane  that 
lines  the  shell. 

6.  Carefully  cut  this  membrane  and  note  that  the  liquid  con- 
tents of  the  egg  do  not  completely  nil  the  eggshell  in  this 
region.  This  cavity  is  called  the  air  space.  Describe  the 
position  of  this  air  space. 

shell 

volk 


white 
of  egg 


FIG.  52.  —  Egg  of  a  hen. 


70 


ANIMAL  BIOLOGY 


3.  Pick  off  the  pieces  of  shell  and  allow  all  the  contents  of  the  shell 

to  flow  out  into  a  cup  or  deep  saucer,  taking  care  not  to 
break  the  yolk. 

a.  State  what  has  been  done,  and  describe  the  position  and  color 

of  the  white  and  of  the  yolk  of  the  egg. 

b.  Note  two  twisted  strands  extending  from  the  yolk  towards 

each  end  of  the  egg.  These  help  to  protect  the  yolk  from 
sudden  jars.  Describe  the  position,  appearance,  and  use 
of  these  strands. 

4.  Carefully  turn  the  yolk  until  you  notice  a  white  spot.     This  spot 

is  the  beginning  of  an  embryo  chick. 
Describe  the  position  and  appearance  of  a  young  chick  embryo. 

54.    Reproduction   and   life   history.  —  In   the   preceding 
section  we  have  seen  that  a  bird's  egg  consists  of  a  hard 

shell,  a  membrane,  the  white 
and  the  yolk ;  and  that  on  the 
outer  surface  of  the  latter  is  a 
tiny  embryo.  Let  us  now  see 
how  this  egg  is  formed  and 
developed. 

In  our  study  of  seed-plants 
we  learned  that  plant  em- 
bryos are  formed  in  the  ovary 
of  a  pistil  after  an  egg-cell 
has  been  fertilized  by  a  sperm- 
cell.  In  the  case  of  insects  (22,  27)  and  the  fish  (104) 
we  find  that  egg-cells  are  produced  in  organs  of  the  female 
known  as  ovaries  and  that  before  an  egg-cell  can  develop 
into  an  embryo  (except  in  rare  cases)  it  must  be  fertilized 
by  a  sperm-cell  (Fig.  53)  which  has  been  formed  in  the 
spermary  of  a  male. 

If  the  ovaries  of  a  hen  are  examined,  they  will  be  found 
to  consist  of  a  large  number  of  spherical  objects,  the  larger 


FIG.  53.  —  Sperm-cells  of  various 
animals. 


BIPDS 


71 


ones  being  yellow,  which  vary  in  size  from  tiny  dots  to  full- 
sized  yolks  (Fig.  54) .  If  any  one  of  these  is  examined  care- 
fully with  a  microscope,  a  single  egg-cell  may  be  found.  After 
the  yolk  has  attained  its  full  size  and  the  egg-cell  has  been 


FIG.  54.  —  Ovary  of  hen,  and  egg  in  egg-tube. 

fertilized,  it  receives  its  coating  of  white,  and  the  whole  is 
covered  with  the  membranes  and  the  shell. 

Immediately  after  fertilization  takes  place,  by  the  process 
of  cell  division  many  cells 
are  formed.  At  the  time 
the  egg  is  laid,  the  chick 
embryo  appears  as  a  tiny 
white  spot  on  the  surface 
of  the  yolk  when  the  egg 
is  opened  (53,  4).  Fur- 
ther development  of  this 
embryo,  however,  can- 
not take  place  unless  the 

egg  is  kept  Warm.      This 


is  brought  about  when 


FlG-   55-  —  Egg  of 

"  ""*** 


hen,   showing  embryo 

(Beebe'"The 


72 


ANIMAL  BIOLOGY 


the  hen  broods  over  the  eggs.  Gradually  the  cells  of  the 
different  external  and  internal  organs  are  formed  (Fig.  55) 
from  the  food  material  furnished  by  the  yolk  and  the  white 
of  the  egg,  and  at  the  end  of  three  weeks  the  young  chick 
breaks  through  the  shell,  and  soon,  under  the  protection  of 
the  mother  hen,  begins  to  search  for  food.  When  first 
hatched,  the  feathers  are  relatively  small  and  downy.  The 
further  development  of  the  chick  is  largely  a  matter  of 
growth  in  size  and  of  change  in  the  character  of  the  feathers. 

55.    Nests  and  care   of  young.  —  The  method  of  repro- 
duction in  all  birds  is  much  the  same  as  that  already  described 


FIG.  56.  —  Comparative  size  of  the  eggs  of  ostrich,  hen,  and  humming 
bird.     (Photographed  by  E.  R.  Sanborn,  N.  Y.  Zoological  Park.) 

for  the  chick.  Many  birds,  however,  are  much  more  help- 
less when  they  emerge  from  the  egg  than  are  chickens,  and 
so  they  are  sheltered  in  nests,  and  the  food  of  the  young 
birds  is  brought  to  them  by  their  parents  until  they  are 
able  to  fly  and  for  several  days  afterwards. 


BIRDS 


73 


Nests  differ  greatly  in  their  complexity  and  in  the  kind  of 
material  used.  Some  birds,  for  example  the  gulls  and  many 
other  sea-birds,  usually  deposit  their  eggs  on  rocky  ledges  or 
in  slight  depressions  in  the  sand  along  the  shore.  On  the 
other  hand,  the  Baltimore  oriole  constructs  out  of  grasses,  plant 
fibers,  and  strings  a  marvelous  nest  hanging  high  up  in  the 
trees,  near  the  outer  ends  of  branches  (Fig.  73).  Between 
these  two  extremes  are  all  gradations  of  nest  complexity. 

The  eggs  laid  by  birds  vary  in  number,  size,  and  color. 
The  tiny  humming  bird,  for 
instance,  lays  two  white 
eggs,  each  a  third  of  an  inch 
in  diameter  (Fig.  56)  ;  three 
to  five  greenish  blue  eggs, 
each  nearly  an  inch  in 
diameter,  are  usually  found 
in  a  robin's  nest,  while  an 
ostrich  deposits  twelve  to 
fourteen  eggs,  each  weigh- 
ing three  to  four  pounds. 


56.  Common  methods  of 
classification.  —  One  of  the 
simplest  ways  of  classifying 
birds  is  that  of  dividing  them 
into  groups  according  to  the 
kind  of  food  they  eat.  For 
instance,  we  may  speak  of  fish- 
eating,  seed-eating,  and  insect- 
eating  birds.  This,  however, 
is  far  from  being  a  scientific 

classification,  since  birds   that 
,.~  .  .       ,  .        . 

diner    considerably    in    struc- 

ture,  and    therefore   not    closely    related,   frequently    live    upon 
the  same  kind  of  food.     For  example,  both  the  pelican  (Fig.  57) 


FlG-   57'™TheT,  p^an>     (phot°- 
graphed  by  E.  R.  Sanborn.) 


FIG.  58.  —  Belted  kingfisher.     (Wright's  "  Citizen  Bird.") 


FIG.  59.  —  Herring  gull.     (Wright's  "  Citizen  Bird.") 


BIRDS 


75 


and  kingfisher  (Fig.  58)  catch  and  eat  fish  for  food,  yet  a  glance  at 
the  two  figures  shows  how  unlike  in  form  these  two  birds  are. 

A  second  scheme  of  classification  is  that  based  upon  their  habitat. 
Thus  we  may  speak  of  water  birds,  shore  birds,  marsh  birds,  and  land 
birds.  This  plan,  too,  may  group  together  birds  strikingly  unrelated 
in  structure  and  habits,  as  becomes  clear  when  we  compare  two 
land  birds  like  the  hawk  (Fig.  64),  and  the  sparrow  (Fig.  70). 

57.  Scientific  classification  of  birds.  —  Modern  scientific  classi- 
fication divides  the  birds  of  North  America  into  seventeen  groups  or 


FIG.  60.  —  Blue  heron.     (Wright's  "  Citizen  Bird.") 

orders,  all  the  birds  of  a  given  order  resembling  each  other  more  or 
less  in  structure.  The  common  names  given  to  some  of  these  orders 
are  suggested  by  their  habits.  As  examples  we  may  name  diving 
birds  (loon),  long-winged  swimmers  (gulls  and  terns),  scratching 
birds  (hens,  turkeys,  and  quails),  birds  of  prey  (eagles,  hawks,  and 
owls),  and  woodpeckers  (downy  woodpecker).  The  highest  order, 
known  as  the  perching  birds,  is  divided  into  twenty  families,  some  of 
which  are  the  crow  family,  the  sparrow  family,  the  warbler,  and  the 


76 


ANIMAL  BIOLOGY 


thrush  family.  The  total  number  of  species  of  the  perching  birds  is 
far  greater  than  that  of  all  other  species  taken  together.  We  shall 
now  group  together  a  few  of  the  more  closely  related  orders,  and 
discuss  somewhat  their  characteristic  adaptations  of  structure. 


FIG.   61.  —  Flamingoes.     (Photographed  in  N.  Y. 
Zoological  Park,  by  E.  R.  Sanborn.) 

58.    Webfooted   birds    (swimming    birds).  —  In   this   group  we 
include  several  orders  of  birds  that  have  webbed  feet,  which  fit  them 


BIRDS 


77 


for  swimming  in  the  water.  Common  examples  of  such  birds  are 
ducks,  geese,  albatross,  and  gulls  (Fig.  59).  Near  the  tail  region  of 
most  of  these  birds  an  oil  gland  is  developed,  from  which  the  bird 
obtains  the  oil  that  it  uses  in  keeping  its  feathers  from  getting 
water-soaked ;  this  is  likewise  true  of  all  other  birds.  As  one  would 
expect,  a  large  number  of  these 
species  feed  upon  fish  and  other 
water  animals. 

59.    Wading    birds.  —  All    the 

birds  in  this  group  have  long,  slen- 
der legs,  which  adapt  them  for 
wading  out  into  the  water  for  food. 
Such  birds  are  the  herons  (Fig.  60), 
egrets,  storks,  and  cranes.  The 
flamingoes  (Fig.  61)  have  webbed 
feet  like  swimming  birds,  and  so  they 
are  regarded  as  connecting  links  be- 
tween swimming  and  wading  birds. 

™ ,.  FIG.  62 .  —  Bobwhite. 

60.     Scratching    birds. —  Inis 

group  includes  the  domesticated  chicken  and  turkey  and  the  quail 
(Fig.  62) .     All  our  various  forms  of  chickens  are  descended  from  the 


FIG.  63.  —  Male  and  female  jungle  fowl.     (Photographed  by  E.  R.  Sanborn, 
from  specimens  of  the  American  Museum  of  Natural  History.) 


78 


ANIMAL   BIOLOGY 


small  jungle  fowl  of  India  (Fig.  63).  The  wild  turkey  still  exists  in 
some  parts  of  our  country,  but  it  is  being  rapidly  exterminated  by 
hunters.  The  toes  of  all  the  scratching  birds  are  armed  with  strong, 
blunt  nails,  by  which  they  are  enabled  to  dig  in  the  soil  for  insects 
and  worms.  All  these  birds,  too,  feed  to  some  extent  upon  grain. 


FIG.  64.  — Red-shouldered  hawk. 


61.  Birds  of  prey.  —  The  hawks  (Fig.  64),  eagles,  and  owls  (Fig. 
65),  which  comprise  this  group  have  acquired  the  name  of  birds  of 
prey  from  their  habit  of  catching  and  feeding  on  rats,  mice,  birds, 
and  other  animals.  Their  feet  are  armed  with  sharp  incurved  claws, 
and  the  upper  part  of  their  bills  is  hooked ;  and  so  they  are  specially 
adapted  for  seizing  and  tearing  their  prey. 


BIRDS 


79 


62.  Woodpeckers.  —  These  birds  are  admirably  adapted  to  creep 
and  climb  up  the  trunks  of  trees,  for  they  have  two  clawed  toes 
extending  forward,  and  two  backward,  and  their  tail  feathers  are  so 
stiffened  that  they  serve  as  props  against  the  bark  when  the  bird  is 
resting  (Fig.  66).  The  food  of  the  woodpeckers  is  largely  com- 
posed of  insects,  which  these  birds  secure  by  digging  them  out  of  the 

bark  or  the  wood  with  their 
stout,  chisel-like  bills,  and 
then  spearing  them  with 
their  long  tongues. 


FIG.  65. — Short-eared  owl.     (Wright.) 


FIG.  66. — Downy  woodpecker. 
(Wright.) 


63.  Perching  birds.  —  This  order,  as  we  have  said  before,  con- 
tains by  far  the  largest  number  of  species  of  birds.  All  these  birds 
are  specially  adapted  for  holding  to  the  limbs  of  trees,  since  the  mech- 
anism of  the  leg  is  so  arranged  that  the  toes  are  automatically 
clutched  to  the  support  upon  which  the  bird  is  sitting.  In  this 
group  are  included  practically  all  of  our  bird  vocalists,  hence  the 
perching  birds  are  often  called  the  "  song  birds."  Among  the  most 
beautiful  of  our  songsters  are  the  bobolinks  (Fig.  67),  catbird,  and 
thrushes  (Fig.  68). 

The  young  of  all  the  perching  birds,  for  weeks  after  they  are 


80 


ANIMAL  BIOLOGY 


hatched,  are  helpless  in  the 
nests  and  are  unable  to  feed 
themselves.  Most  of  the 
food  of  young  birds  consists 
of  the  larvae  of  insects  and 
some  of  the  families,  e.g.  the 
fly-catchers  (Fig.  69),  feed 
upon  insect  food  through- 
out their  life.  The  sparrow 
family  (Fig.  70),  on  the  other 
hand,  choose  largely  a  diet  of 
seeds.  Almost  every  kind  of 
food,  however,  is  eaten  by 
some  of  the  perching  birds. 


64.  Migration  of  birds.  — 
Some  of  the  birds  like  the 
chickadee  and  downy  woodpecker,  remain  in  the  middle  and  northern 
United  States  throughout  the  year,  and  hence  are  known  as  permanent 
residents  of  these  regions.  Many  birds,  however,  spend  the  winter 


FIG.  67.  —  Male  and  female  bobolink. 


FIG.  68.— Wood  thrush. 


BIRDS 


81 


in  the  warmer  regions 
of  the  South  and  in  the 
spring  months  move 
northward;  some  of 
them,  like  the  robin 
(Fig.  71)  and  the  blue- 
bird, build  their  nests, 
rear  their  young,  and 
stayall  summer  in  north- 
ern and  middle  United 
States.  Such  birds  are 
called  summer  residents. 
Still  other  birds  rear 
their  young  in  Canada 
and  even  farther  north, 
and  come  to  us  only  as  FIG.  69.  —  Kingbird. 
winter  visitants.  This 
seasonal  movement  of  birds  is  known  as  migration. 


(Courtesy  of  National 
Audubon  Society.) 

Migration  is 


/f 


FIG.  70.  —  Tree  sparrow.     (Courtesy  of  National  Audubon  Society.) 
G 


82 


ANIMAL   BIOLOGY 


especially  characteristic  of  the  perching  birds.     For  this  reason,  the 
birds  in  this,  the  highest  order,  are  known  as  "  birds  of  passage." 


FIG.  71.  —  The  robin. 


DATE 
WHEN 

SEEN 

PLACE 
WHERE  SEEN 

SiZE1  COMPARED 
TO  ROBIN  OR 
SPARROW 

COLOR  OF 
BACK 

COLOR  OF 
BREAST 

STRIK- 
ING 
COLORS 

NAME 

OF 

BIRD 

Mar.  10, 

Lower  limbs 

Larger  than 

Bright 

Reddish 

Belly 

Blue- 

1912 

of  trees 

sparrow 

blue 

brown 

white 

bird 

66.  Field  work  on  birds.  —  Pupils  should  become  familiar  with 
the  size,  form,  colors,  and  song  of  as  many  birds  as  possible,  and 
should  note  carefully  where  each  kind  of  bird  is  most  commonly 
found  (e.g.  in  marshes,  trees,  bushes,  or  on  the  ground).  In  this 
study  bird  glasses  or  opera  glasses  are  very  useful.  Books  like 

1  Length  of  robin  from  tip  of  bill  to  tip  of  tail  feathers,  about  10 
inches ;  length  of  sparrow  from  tip  of  bill  to  tip  of  tail  feathers, 
about  6  inches. 


BIRDS  83 

Chapman's  "  Bird  Life,"  Wright's  "  Citizen  Bird  "  and  "  Birdcraft," 
Hornaday's  "  American  Natural  History,"  should  be  frequently 
consulted.  In  order  to  record  striking  characteristics  as  a  help 
toward  identifying  birds,  it  is  suggested  that  each  pupil  fill  out  a 
table  as  shown  on  page  82. 

66.  Importance  of  birds  to.  man.  —  Few  animals  are  more 
beautiful  in  form  and  color  than  are  many  of  our  most  com- 
mon birds,  and  one  of  the  greatest  delights  of  springtime 
is  to  greet  the  return  of  the  bluebirds,  tanagers,  thrushes, 
and  others  of  our  feathered  friends.  "  To  appreciate  the 
beauty  of  form  and  plumage  of  birds,  their  grace  of  motion 
and  musical  powers,  we  must  know  them.  .  .  .  Once  aware 
of  their  existence,  and  we  shall  see  a  bird  in  every  bush  and 
find  the  heavens  their  pathway.  One  moment  we  may 
admire  the  beauty  of  their  plumage,  the  next  marvel  at  the 
ease  and  grace  with  which  they  dash  by  us  or  circle  high  over- 
head. .  .  .  The  comings  and  goings  of  our  migratory  birds 
in  springtime  and  fall,  their  nest-building  and  rearing  of 
young,  their  many  regular  and  beautiful  ways  as  exhibited  in 
their  daily  lives,  stir  within  us  impulses  for  kindness  toward 
the  various  creatures  which  share  the  world  with  us.  ... 
But  birds  will  appeal  to  us  most  strongly  through  their  song. 
When  your  ears  are  attuned  to  the  music  of  birds,  your  world 
will  be  transformed.  Birds'  songs  are  the  most  eloquent  of 
Nature's  voices :  the  gay  carol  of  the  grosbeak  in  the  morn- 
ing, the  dreamy,  midday  call  of  the  pewee,  the  vesper  hymn 
of  the  thrush,  the  clanging  of  geese  in  springtime,  the  farewell 
of  the  bluebird  in  the  fall,  —  how  clearly  each  one  expresses 
the  sentiment  of  the  hour  or  season ! "  —  Quoted  from 
Bulletin  No.  3  of  University  of  Nebraska,  and  from  Chap- 
man's "  Bird  Life." 

The  value  of  birds  to  man  as  objects  of  beauty  cannot  be 
measured,  it  is  true,  in  dollars  and  cents;  but  were  we  to 


84 


ANIMAL  BIOLOGY 


lose  the  birds,  we  should  realize  all  too  well  how  much  they 
contribute  to  the  happiness  of  every  lover  of  nature.  When, 
however,  we  come  to  discuss  the  economic  value  of  birds, 
the  good  that  they  do  cannot  be  overestimated.  Biologists 
have  carried  on  long  series  of  studies  to  determine  accurately 
the  food  of  different  kinds  of  birds.  This  has  been  done 

by     watching     them 
while  they  are  eating 
or  while  feeding  their 
young,   and  by  examin- 
ing the  contents  of  birds' 
stomachs.      The    following 
paragraphs    contain    descrip- 
tions of  some  of  the  ways  in 
which  birds  are  of  inestima- 
ble use  to  man. 

67.  Birds  as  destroyers  of  harmful 
insects. — Undoubtedly  the  greatest  value 
of  birds  to  man  is  the  good  that  they  do  in 
destroying  injurious  insects.  In  13-18,  23, 
and  46,  we  have  described  some  of  the 
ravages  made  by  our  insect  foes. 

"  But  if  insects  are  the  natural  enemies 
of  vegetation,  birds  are  the  natural  enemies  of  insects.  .  .  . 
In  the  air  swallows  and  swifts  are  coursing  rapidly  to  and  fro, 
ever  in  pursuit  of  the  insects  which  constitute  their  sole  food. 
When  they  retire,  the  nighthawks  and  whip-poor-wills  will  take 
up  the  chase,  catching  moths  and  other  nocturnal  insects 
which  would  escape  day-flying  birds.  Fly-catchers  (Fig.  69) 
lie  in  wait,  darting  from  ambush  at  passing  prey,  and  with 
a  suggestive  click  of  the  bill  returning  to  their  post.  The 
warblers  (Fig.  72),  light,  active  creatures,  flutter  about  the 


FIG.     72.  —  Black 
and  white  warbler. 


BIRDS  85 

terminal  foliage,  and  with  almost  the  skill  of  a  humming 
bird,  pick  insects  from  the  leaf  or  blossom.  The  vireos 
patiently  explore  the  underside  of  leaves  and  odd  nooks  and 
corners  to  see  that  no  skulker  escapes.  The  woodpeckers 
(Fig.  66),  nuthatches,  and  creepers  attend  to  the  trunks  and 
limbs,  examining  carefully  each  inch  of  bark  for  insects' 
eggs,  and  larvae,  or  excavating  for  the  ants  and  borers  they 
hear  within.  On  the  ground  the  hunt  is  continued  by  the 
thrushes  (Fig.  68),  sparrows  (Fig.  70),  and  other  birds  that 
feed  upon  the  innumerable  forms  of  terrestrial  insects.  Few 
places  in  which  insects  exist  are  neglected;  even  some 
species  which  pass  their  earlier  stages  or  entire  lives  in  the 
water  are  preyed  upon  by  aquatic  birds."  1  —  From  CHAP- 
MAN'S "  Bird  Life." 

As  examples  of  the  number  of  insects  destroyed  by  in- 
dividual birds  we  may  give  the  following:  Six  robins  in 
Nebraska  ate  265  Rocky  Mountain  locusts ;  the  stomachs 
of  four  chickadees  contained  1028  eggs  of  cankerworms ; 
101  potato  beetles  were  found  in  the  stomach  of  a  single 
quail  (Fig.  62) ;  and  250  hairy  caterpillars,  which  other 
birds  do  not  eat,  were  devoured  by  a  yellow-billed  cuckoo. 
(Frontispiece.) 

68.  Birds  as  destroyers  of  weed  seeds.  —  Another  way 
in  which  birds  are  useful  to  man  is  in  the  destruction  of  weed 
seeds.  Most  perching  birds  that  feed  largely  upon  seeds, 
e.g.  the  sparrows  and  finches,  have  stout,  conical  bills  (Fig. 
70)  which  are  specially  adapted  for  crushing  seeds.  In  one 
of  the  pamphlets  of  the  United  States  Department  of  Agri- 
culture, entitled  "  Some  Common  Birds  and  their  Relation 

1  Before  assigning  this  section  for  study  each  of  the  birds  named 
should  if  possible  be  shown  to  the  class,  or  at  least  colored  pictures 
of  the  birds,  e.g.  in  Chapman's  "Bird  Life." 


86 


ANIMAL  BIOLOGY 


FIG.  73.  —  Nest  of  Baltimore  oriole  ;  male  bird  below,  female  above.    (Photo- 
graphed by  A.  E.  Rueff  of  the  Brooklyn  Institute  of  Arts  &  Sciences.) 


BIRDS  87 

to  Agriculture,"  the  writer  estimated  that  in  the  state  of 
Iowa  during  the  six  months  of  fall  and  winter,  tree  sparrows 
devoured  875  tons  of  weed  seed.  An  actual  count  of  the 
stomach  contents  of  a  bobwhite  showed  the  presence  of 
400  pigweed  seeds.  In  the  stomach  of  another  were  500 
seeds  of  ragweed. 

69.  Birds  as  destroyers  of  rats  and  mice.  —  We  learned 
in  61  that  hawks  and  owls  by  their  hooked  bills  and  claws 
are  admirably   fitted  to    clutch   and  tear   living   prey.     It 
has  been  demonstrated  that  the  food  of  many  of  these  birds 
consists   almost  wholly    of  small  gnawing    mammals   (e.g. 
field  mice)  (Fig.  64)  which  are  exceedingly  injurious  in  fields 
of  grain.     An  examination  of  the  stomachs  of  fifty  short- 
eared  owls  (Fig.  65)  showed  that  90  per  cent  of  them  contained 
nothing  but  mice.     Forty  of  the  forty-nine  stomachs  of  the 
rough-legged  hawks  were  found  to  contain  mice,  while  most 
of  the  rest  contained  injurious  animals. 

70.  Birds  as  scavengers.  —  Some  birds  of  prey,  like  the 
turkey  buzzards  of  the  Southern  states,  eat  animals  that  are 
dead.     "  These  animals  may  be  seen  at  all  hours  of  the  day 
sailing  through  the  air  in  majestic  circles  or  lazily  resting 
on  stumps  or  trees  after  a  feast  of  their  filthy  food.     They 
perform  an  important  service  as  scavengers,  disposing  of  all 
sorts  of  animal  matter  that  would  pollute  the  air.     On  this 
account  they  are  seldom  molested  by  man  and  in  some 
States  are  protected  by  law.     They  devour  both  fresh  and 
putrid  meat.  .  .  .     They  are  known  sometimes  to  capture 
live  snakes  and  to  attack  helpless  animals  of  many  kinds. 
Along  the  seashore  they  feed  upon  dead  fish  cast  up  by  the 
waves."    -  WEED  and  DEARBORN,  "  Birds  in  their  Relations 
to  Man."     Gulls  (Fig.  59)  also  serve  a  useful  purpose  by 


88  ANIMAL   BIOLOGY 

devouring  dead  fish  and  other  refuse  along  our  coast  line 
and  in  our  harbors. 

71.  Birds  injurious  to  man.  —  We  have  discussed  briefly 
in  the  preceding  sections  some  of  the  ways  in  which  birds 
are  of  incalculable  value  to  man.  It  must  be  admitted, 
however,  that  some  birds  are  of  doubtful  value,  while  others 
are  positively  injurious.  As  an  ,example  of  a  bird,  which, 
to  say  the  least,  is  a  nuisance,  we  may  mention  the  common 
English  sparrow.  This  bird  was  first  introduced  from  Eng- 
land into  the  United  States  in  Brooklyn,  N.  Y.,  in  1851, 
because  it  was  expected  to  attack  some  of  our  injurious  in- 
sects. These  sparrows  have  multiplied  so  rapidly  that  now 
they  are  found  practically  everywhere  in  the  United  States. 
"  As  destroyers  of  noxious  insects,  the  sparrows  are  worse 
than  useless."  Thus,  for  instance,  the  stomach  of  a  single 
cuckoo  (Frontispiece)  was  found  to  contain  more  insects  than 
did  the  stomachs  of  522  English  sparrows. 

But  even  more  serious  are  the  positive  charges  that  have 
been  proved  against  this  bird.  It  pecks  at  and  destroys 
the  young  buds  of  trees,  and  later  injures  many  fruits  while 
they  are  ripening.  It  causes  great  losses  in  the  grain  fields 
from  the  time  of  planting  to  that  of  harvesting;  and  worst 
of  all  is  the  fact  that  it  molests  and  drives  away  our  native 
song  and  insect-eating  birds. 

The  crow  (Fig.  74)  is  another  bird  that  on  the  whole  is 
probably  more  injurious  than  beneficial  for  the  following 
reasons :  "  (1)  Crows  seriously  damage  the  corn  crop,  and 
injure  other  grain  crops,  usually  to  a  less  extent.  (2)  They 
damage  other  farm  crops  to  some  extent,  frequently  doing 
much  mischief.  (3)  They  are  very  destructive  to  the  eggs 
and  young  of  domesticated  fowls.  (4)  They  do  incalculable 
damage  to  the  eggs  and  young  of  native  birds.  (5)  They 


BIEDS  89 

do  much  harm  by  the  distribution  of  seeds  of  poison  ivy, 
poison  sumach,  and  perhaps  other  noxious  plants.  (6)  They 
do  much  harm  by  the  destruction  of  beneficial  insects.  On 
the  other  hand  :  (1)  They  do  much  good  by  the  destruction 
of  injurious  insects.  (2)  They  are  largely  beneficial  through 
their  destruction  of  mice  and  other  rodents.  (3)  They  are 
valuable  occasionally  as  scavengers."  —  W.  B.  BARROWS, 
"  The  Food  of  Crows." 


FIG.  74. —  The  crow. 

While  most  of  the  hawks  are  undoubtedly  beneficial  (69), 
two  species,  namely,  Cooper's  hawk  and  the  sharp-shinned 
hawk,  must  be  kept  down  to  limited  numbers.  Both  of 
these  are  "  chicken-hawks,"  and  in  addition  they  ruthlessly 
destroy  great  numbers  of  our  most  valuable  wild  birds. 

72.    Summary  of  the  relation  of  birds  to  human  welfare.  — 

Library  study. 

For  further  facts  like  the  following,  consult,  Weed  and  Dear- 


90 


ANIMAL   BIOLOGY 


born's  "  Birds  and  their  Relation  to  Man,"  Forbush's 
"  Useful  Birds  and  their  Protection,"  Hornaday's  "  American 
Natural  History,"  pamphlets  of  Department  of  Agriculture 
(which  may  be  obtained  free  from  Washington,  D.C.,  and 
from  State  Departments  of  Agriculture),  and  articles  on 
birds  and  insects  in  Encyclopedias. 


NAME  OF  BIKD 

TIME  OF 
VISITATION 

KIND  OF  ANIMAL 
FOOD  EATEN 

KIND  OF 
VEGETABLE  FOOD 
EATEN 

REMARKS 

Robin      .     .    . 

Summer 

Insects,  42 

Small  fruits 

Beneficial 

resid. 

per  cent 

and  berries, 

mostly  wild, 

58  per  cent 

Phoebe    .    .    . 

Summer 

Insects 

Wild  fruits, 

Beneficial 

resid. 

caught  on 

7  per  cent 

wing,  93 

per  cent 

Hairy    wood- 

Perm. 

Wood-bor- 

Wild fruits 

Beneficial 

pecker  .     .     . 

resid. 

ing  insects 

and  ants 

Yellow  -billed 

Summer 

Insects, 

Beneficial 

cuckoo      .    . 

resid. 

largely 

hairy 

„ 

caterpillars 

Quail   or   bob- 

Perm. 

Insects  in 

Weed  seeds 

Beneficial 

white    .     .     . 

resid. 

summer 

during  rest 

of  year 

Tree  sparrow  . 

Winter 

Weed  seeds 

Beneficial 

visit. 

Bobolink     .    . 

Summer 

Insects  in 

Rice  in  South 

$2,000,000 

resid. 

North 

loss  to 

rice  crop 

Short-eared  owl 

Perm. 

Rats,  mice 

Beneficial 

resid. 

and  other 

small 

mammals 

BIRDS 


91 


NAME  OF  BIRD 

TIME  OF 

VISITATION 

KIND  OF  ANIMAL 
FOOD  EATEN 

KIND  OF 
VEGETABLE  FOOD 
EATEN 

REMARKS 

Sparrow-hawk 

Summer 

Mice  and 

Beneficial 

resid. 

insects 

Cooper's  hawk 

Summer 

Poultry  and 

Injurious 

resid. 

song  birds 

Sharp  -shinned 

Summer 

Poultry  and 

Injurious 

hawk    .     .     . 

resid. 

song  birds 

Crow  .... 

Perm. 

Insects, 

Corn  and 

Doubtful 

resid. 

mice, 

other  crops, 

value 

eggs  and 

weed  seeds 

young  of 

other  birds 

English     spar- 

Perm. 

Insects 

Buds,  fruit, 

Drives 

row  .... 

resid. 

rarely 

grain 

away 

useful 

birds 

73.  Causes  of  decrease  in  bird  life.  —  Certainly  enough 
has  been  said  to  show  that  when  all  things  are  considered 
birds  are  exceedingly  useful  to  man.  One  would  therefore 
expect  that  every  possible  means  would  be  taken  to  protect 
all  kinds  of  valuable  birds.  Yet  what  do  we  find  ?  "  To- 
day the  first  thing  to  be  taught  is  the  fact  that  from  this 
time  henceforth  all  birds  must  be  protected,  or  they  will  all 
be  exterminated.  To-day,  it  is  a  safe  estimate  that  there  is 
a  loaded  cartridge  for  every  living  bird.  Each  succeeding 
year  produces  a  new  crop  of  gun-demons,  eager  to  slay,  am- 
bitious to  make  records  as  sportsmen  or  collectors.  If  a 
bird  is  so  unfortunate  as  to  possess  plumes,  or  flesh  which 
can  be  sold  for  ten  cents,  the  mob  of  pot-hunters  seeks  it 
out,  even  unto  the  ends  of  the  earth."  -  HORNADAY'S  "The 
American  Natural  History." 

A  careful  investigation  made  in  1897  for  the  New  York  Zoo- 


92  ANIMAL   BIOLOGY 

logical  Society  showed  that  during  the  fifteen  years  between 
1883  and  1898  in  all  but  four  states  l  the  number  of  birds  had 
strikingly  decreased:  For  example,  in  New  York  State  the 
decrease  was  48  per  cent,  or  almost  one  half ;  in  Florida  it 
was  over  three  fourths,  while  the  average  for  the  whole 
country  was  46  per  cent.  Among  the  principal  reasons 
given  by  the  180  careful  observers  who  assisted  Dr.  Hornaday 
in  the  foregoing  inquiry  were  the  following :  "  (1)  sportsmen 
and  so-called  sportsmen,  (2)  boys  who  shoot,  (3)  market 
hunters  and  pot-hunters,  (4)  plume-hunters  and  milliners' 
hunters,  ...  (6)  egg-collecting,  chiefly  by  small  boys, 
(7)  English  sparrow,  ...  (9)  Italians,  and  others,  who 
devour  song  birds." 

74.  Destruction  of  birds  by  cats.  —  "  As  the  cat  is  not 
an  actual  necessity,  and  as  it  is  a  potent  carrier  of  contagious 
diseases,  which  it  spreads,  particularly  among  children,  it 
would  be  far  better  for  the  community  if  most  of  the  bird- 
killing  cats  now  roaming  at  large  could  be  painlessly  dis- 
posed of.  ...     Where  the  cat  is  deemed  necessary  in  farm 
or  village,  no  family  should  keep  more  than  one  good  mouser, 
which  should  never  be  allowed  to  have  its  liberty  during  the 
breeding  season  of  birds.  .  .  .     Cats  can  be  confined  during 
the  day  in  outdoor  cages  as  readily  as  rabbits,  and  given 
the  run  of  the  house  at  night."  —  FORBUSH,  "  Useful  Birds 
and  their  Protection." 

75.  Destruction   of   birds   by   boys.  —  One   of  the   most 
serious  menaces  to  our  native  bird  life  is  the  small  boy  who 
has  the  "  egg-collecting  fever."     All  the  eggs  he  can  find  in 
his  keen-eyed  searches  through  the  woods  and  fields  are 

1  Kansas,  Wyoming,  Utah,  and  Washington  were  the  only  states 
that  showed  an  increase  in  bird  life. 


BIBBS  93 

destroyed  to  increase  his  collection.  If  this  served  any  really 
useful  purpose,  the  resulting  wholesale  destruction  of  birds 
might  possibly  have  some  justification.  But  ninety-nine 
out  of  a  hundred  of  these  collections  are  soon  forgotten  and 
become  useless  without  having  made  any  real  contribution 
to  the  knowledge  of  the  possessor. 

The  small  boy,  too,  unfortunately  carries  his  destructive 
work  among  birds  still  further,  as  the  following  typical  inci- 
dent will  show.  A  biologist  reports  meeting  near  Washing- 
ton, D.C.,  "  one  such  youngster,  and  upon  examining  his 
game  bag  found  it  absolutely  full  of  dead  bodies  of  birds 
which  he  had  killed  since  starting  out  in  the*  morning.  One 
item  alone  consisted  of  seventy-two  ruby  and  golden-crowned 
kinglets.  The  fellow  boasted  of  having  slain  over  one 
hundred  catbirds  that  season." 

76.  Destruction  of  birds  for  food.  —  In  the  early  days  of 
the  white  settlements  in  North  America,  the  game  birds  like 
the  grouse  and  duck  were  abundant  and  they  were  of  neces- 
sity killed,  as  were  other  wild  animals,  for  food.  Later  on 
began  the  killing  of  birds  for  sport.  As  the  forests  were 
cut  down,  the  birds  had  less  and  less  protection,  and  had  not 
legislation  intervened,  the  game  birds  would  long  since  have 
been  exterminated.  As-  it  is,  they  have  been  killed  faster 
than  they  breed ;  and  this  means  ultimate  extermination. 

To  this  destruction  of  game  birds  for  food,  in  more  recent 
times  has  been  added  the  wholesale  slaughter  of  many  of 
our  smaller  birds  like  the  thrushes,  sparrows,  warblers,  and 
woodpeckers.  It  is  claimed  that  this  has  been  largely  due 
to  the  demands  of  our  immigrant  population  in  the  North 
and  to  the  negroes  in  the  South.  "  However,  there  is  scarcely 
a  hotel  in  New  Orleans,"  says  Professor  Nehrling,  "  where 
small  birds  do  not  form  an  item  on  the  bill  of  fare.  At  cer- 


94 


ANIMAL   BIOLOGY 


tain  seasons  the  robin,  wood  thrush,  thrasher,  olive-backed 
thrush,  hermit  thrush,  chewink,  nicker,  and  many  of  our 
beautiful  sparrows  form  the  bulk  of  the  victims;  but  cat- 
birds, cardinals,  and  almost  all  small  birds,  even  swallows, 
can  be  found  in  the  markets." 


77.   Destruction  of  birds  for  millinery  purposes.  —  Even 
more  ruthless  than  the  slaughter  of  birds  for  food  by  boys 

and  by  men  is  that  caused 
by  the  demand  for  birds 
for  millinery  purposes. 
Here  the  final  responsi- 
bility rests  upon  women 
alone.  A  single  dealer 
in  the  South  declared 
that  in  the  course  of  a 
single  year  he  handled 
30,000  bird  skins,  the 
largest  part  of  which 
were  used  in  the  decora- 
tion of  hats. 

The  Florida  egret  heron 
(Fig.  75)  has  been  prac- 
tically exterminated  for 
this  purpose.  "Twenty 
years  ago,"  says  Chap- 
man, "it  was  abundant  in  the  South,  now  it  is  the  rarest 
of  its  family.  The  delicate  '  aigrettes '  which  it  donned  as 
a  nuptial  dress  were  its  death  warrant.  Woman  demanded 
from  the  bird  its  wedding  plumes,  and  man  has  supplied  the 
demand.  The  Florida  herons  or  egrets  have  gone,  and  now  he 
is  pursuing  the  helpless  birds  to  the  uttermost  parts  of  the 
earth.  Mercilessly  they  are  shot  down  at  their  roosts  or 


FIG.   75.  —  Egret,    nest,    and    young. 
(Courtesy  National  Audubon  Society.) 


BIRDS  95 

nesting  grounds,  the  coveted  feathers  are  stripped  from  their 
backs,  the  carcasses  are  left  to  rot,  while  the  young  in  the 
nest  above  are  starving." 

"  This  slaughter  of  the  innocents  is  by  no  means  confined 
to  the  Southern  states.  During  four  months  70,000  bird 
skins  were  supplied  to  the  New  York  trade  by  one  Long 
Island  village.  'On  the  coast  line  of  Long  Island,'  wrote 


FIG.  76. — Tern. 

Mr.  William  Butcher,  not  long  ago,  'the  slaughter  has  been 
carried  on  to  such  a  degree  that,  where,  a  few  years  since, 
thousands  and  thousands  of  terns  (Fig.  76)  were  gracefully 
sailing  over  the  surf-beaten  shore  and  the  wind-rippled  bays, 
now  one  is  rarely  to  be  seen.'  Land  birds  of  all  sorts  have 
also  suffered  in  a  similar  way,  both  on  Long  Island  and  in 
adjacent  localities  in  New  Jersey.  Nor  have  the  interior 
regions  of  the  United  States  escaped  the  visits  of  the  milli- 


96  ANIMAL  BIOLOGY 

ner's  agent.  An  Indianapolis  taxidermist  is  on  record  with 
the  statement  that  in  1895  there  were  shipped  from  that  city 
5000  bird  skins  collected  in  the  Ohio  Valley.  He  adds  that 
'  no  county  in  the  state  is  free  from  the  ornithological  mur- 
derer/ and  prophesies  that  birds  will  soon  become  very  scarce 
in  the  state. 

"  These  isolated  examples  can  only  suggest  the  enormous 
number  of  birds  that  are  sacrificed  on  the  altar  of  fashion. 
The  universal  use  of  birds  for  millinery  purposes  bears  suffi- 
cient testimony  to  the  fact.  Yet  it  is  probable  that  most 
women  who  follow  the  fashion  seldom  appreciate  the  suffer- 
ing and  the  economic  losses  that  it  involves."  —  WEED  and 
DEARBORN,  "  Birds  in  their  Relations  to  Man." 

78.  Effects  of  bird  destruction.  —  While  the  aesthetic 
loss  to  mankind  resulting  from  the  destruction  of  our  wild 
birds  cannot,  as  we  have  said,  be  computed,  yet  even  in  the 
cities  this  loss  is  beginning  to  be  realized  as  we  see  the  song 
birds  in  the  parks  steadily  diminishing  in  number.  Every- 
one, however,  is  affected  by  the  increasing  cost  of  our  food 
supply,  and  we  have  but  to  review  the  facts  stated  in  the 
preceding  sections  to  show  that  the  destruction  of  our  wild 
birds  has  a  very  important  bearing  on  the  present  situa- 
tion. 

Every  farmer  knows  that  it  is  impossible  to  raise  the  crops 
of  a  single  year  without  battling  with  insect  pests.  The 
time  and  expense  involved  in  applying  insect-destroying 
preparations  would  be  difficult  to  compute,  and  even  after 
the.  year's  contest  is  ended,  the  insects  are  often  victorious. 
In  ruthlessly  destroying  the  wild  birds  man  has  interfered 
with  the  "  balance  of  nature"  and  so  has  helped  the  ravaging 
hordes  of  insects  and  gnawing  animals  to  multiply  without 
adequate  check.  All  this  means  that  we,  the  consumers  of 


BIRDS  97 

the  fruits,  the  vegetables,  and  the  grains,  must  pay  higher 
prices  for  the  food  we  eat  and  the  clothes  we  wear. 

79.  Conservation  of  birds.  —  But  it  is  not  yet  too  late 
to  save  the  remnant  of  the  birds  still  left  to  us,  and  even  to 
increase  the  bird  life  of  our  country.  It  is  evidently  neces- 
sary, however,  in  the  first  place,  that  laws  similar  to  the 
following  should  be  passed  in  every  state. 

"  The  Bird  Law  of  the  American  Ornithologists'  Union.  —  An 
Act  for  the  Protection  of  Birds  and  their  Nests  and  Eggs. 

"  Section  1.  —  No  person  shall  within  the  State  of kill  or 

catch  or  have  in  his  or  her  possession,  living  or  dead,  any  wild 
bird  other  than  a  game  bird,  nor  shall  purchase,  offer,  or  expose  for 
sale  any  such  wild  bird  after  it  has  been  killed  or  caught.  No  part 
of  the  plumage,  skin,  or  body  of  any  bird  protected  by  this  section 
shall  be  sold  or  had  in  possession  for  sale. 

"  Section  2.  —  No  person  shall  within  the  State  of take  or 

needlessly  destroy  the  nest  or  the  eggs  of  any  wild  bird  nor  shall 
have  such  nest  or  the  eggs  in  his  or  her  possession.  .  .  . 

"  Section  3.  —  Any  person  who  violates  any  of  the  provisions  of 
this  act  shall  be  guilty  of  a  misdemeanor,  and  shall  be  liable  to  a 
fine  of  five  dollars  for  each  offense,  and  an  additional  fine  of  five  dollars 
for  each  bird,  living  or  dead,  or  part  of  bird,  or  nest  and  eggs  pos- 
sessed in  violation  of  this  act,  or  to  imprisonment  for  ten  days,  or 
both,  at  the  discretion  of  the  court. 

"  Section  4.  —  Sections  1,  2,  and  3  of  this  act  shall  not  apply  to 
any  person  holding  a  certificate  giving  the  right  to  take  birds  and 
their  nests  and  eggs  for  scientific  purposes,  as  provided  for  in  Sec- 
tion 5  of  this  Act.  .  .  . 

"  Section  7.  —  The  English  or  European  house  sparrow  (Passer 
domesticus)  is  not  included  among  the  birds  protected  by  this  act." 

"  In  addition  to  the  above,  every  state  that  has  not 
already  done  so,  should  at  once  enact  laws  to  prohibit  the 
sale  of  all  wild  game  at  all  seasons,  and  to  stop  all  shooting 


98  ANIMAL  BIOLOGY 

of  game  in  late  winter  and  spring.  About  one  half  the 
states  have  done  this,  and  the  other  half  should  act  without 
delay.  The  sale  of  game  has  almost  destroyed  our  once 
magnificent  supply  of  game  birds.  We  have  no  right  to 
hand  down  to  posterity  a  gameless  continent.  The  wild 
life  of  to-day  is  not  wholly  ours  to  dispose  of  as  we  please. 
It  has  been  given  to  us  in  trust.  We  must  account  for  it 
to  those  who  come  after  us  and  audit  our  records."1  —  Dr. 

W.  T.  HORNADAY. 

But  laws,  however  stringent,  are  of  little  avail  unless  there 
is  a  healthy  public  sentiment  to  bring  about  their  enforce- 
ment. Thus,  for  instance,  it  is  evident  that  laws  merely  de- 
signed to  prevent  the  killing  of  birds  for  millinery  purposes 
will  be  ineffective,  so  long  as  women  are  permitted  to  wear 
birds.  One  thing  will  completely  stop  the  cruelty  of  bird 
millinery  —  the  disapprobation  of  fashion.  "It  is  our 
women  who  hold  the  great  power.  Let  our  women  say  the 
word,  and  hundreds  of  bird  lives  will  be  preserved  every 
year.  And  until  woman  does  use  her  influence  it  is  vain 
to  hope  that  this  nameless  sacrifice  will  cease  until  it  has 
worked  out  its  own  end  and  the  birds  are  gone."  -  WEED 
and  DEARBORN,  "  Birds  in  their  Relations  to  Man." 

80.  What  boys  and  girls  can  do  to  protect  birds.  —  "  Now 
that  adequate  statutes  are  either  enacted  or  may  reasonably 
be  expected  very  soon,  it  remains  to  scatter  information 
about  birds  everywhere,  so  that  laws  may  be  respected  .  .  . 
and  it  is  in  this  line  that  those  interested  in  their  conservation 
should  work.  There  must  be  lectures,  short  articles  of  a 
popular  nature  in  newspapers  and  magazines,  distribution 
of  government  and  other  publications  relating  to  birds, 

1  The  authors  are  indebted  to  Dr.  W.  T.  Hornaday,  of  the  New 
York  Zoological  Park,  for  many  suggestions  relating  to  conservation 
of  birds  and  for  a  careful  reading  of  the  chapters  on  birds  and  fishes. 


BIRDS 


99 


posting  bird  laws  in  conspicuous  places,  and  most  important 
of  all,  systematic  bird  work  in  public  schools.  The  impor- 
tance of  engaging  the  interest  of  our  youth  in  birds  cannot 
be  overestimated.  It  results  in  a  double  benefit,  for  the 
birds  will  be  held  in  higher  esteem  and  the  children  will 
become  possessed  of  a  source  of  lasting  pleasure.  The  nest- 
robbing,  bird-shooting  boy  and  the  feather-wearing  girl 
may  be  made  the  friends  and  allies  of  the  birds."  -WEED 
and  DEARBORN,  "  Birds 
in  their  Relations  to 
Man." 

But  not  only  should 
the  boy  cease  to  destroy 
nests  and  shoot  birds; 
not  only  should  the  girl 
cease  to  wear  any  part 
of  a  wild  bird ;  but  boys 
and  girls  alike  should  do 
all  they  can  to  induce 
others  to  do  likewise. 
Much  may  also  be  done, 
likewise,  even  in  the  vicinity  of  large  towns,  to  attract  birds 
and  induce  them  to  nest.  In  the  first  place,  the  nests  and 
eggs  of  the  English  sparrow  should  be  destroyed  whenever 
found.  Stray  cats  should  be  kept  from  harming  birds. 
Pieces  of  meat,  bones,  and  suet,  when  hung  in  the  trees  in 
winter  tune,  and  crumbs  and  grains  scattered  about,  will 
serve  to  attract  the  winter  visitants  and,  when  thus  at- 
tracted, these  birds  devour  great  numbers  of  the  eggs 
and  insects  in  the  hibernating  stages  that  during  the  follow- 
ing season  would  attack  the  fruit  and  shade  trees.  And 
finally,  any  ingenious  boy  can  construct  and  put  in  the 
trees  bird  houses  that  in  the  springtime  would  become  the 


FIG.  77. —  Bird  house  made  by  a  tjvelve- 
year-old  boy. 


100  ANIMAL  BIOLOGY 

nesting  places  of  bluebirds,  wrens,  tree  swallows,  and  martins.1 
(Fig.  77.) 

1  For  other  methods  of  encouraging  birds  see  Weed  and  Dear- 
born, "Birds  in  their  Relations  to  Man,"  pp.  304-315.  Trafton, 
"Methods  of  Attracting  Birds,"  and  leaflets  of  National  Associa- 
tion of  Audubon  Societies,  1974  Broadway,  N.  Y.,  e.g.  No.  16  (Win- 
ter Feeding  of  Wild  Birds)  and  No.  18  (Putting  up  Bird  Boxes),  1 
cent  each. 


CHAPTER  III 
FROGS  AND   THEIR  RELATIVES 

81.    Study  of  the  frog.  —  Laboratory  study. 

A.  Regions  and  appendages.  —  The  frog's  body  consists  of 

two  principal  parts,  or  regions ;  namely,  the  head 
and  trunk.  The  line  of  union  between  the  two 
regions  is  just  in  front  of  the  anterior  append- 
ages (arms). 

1.  Locate  the  appendages  (arms  and  legs)  attached  to 

the  trunk. 

2.  Name  and  locate  the  organs  that  you  find  on  the 

head,  giving  the  number  of  each. 

B.  Breathing  organs. 

1.  Describe  the  location  of  the  nostrils  on  the  head. 

2.  Examine  a  preserved  specimen  in  which  a  stiff  bristle 

has  been  passed  through  one  of  the  nostrils. 
a.   Tell  what  was  done. 
6.   Into  what  cavity  has  the  bristle  emerged? 

c.  (Optional.)    What  is  one  difference,  therefore,  between 

the  nostrils  of  a  fish  and  of  a  frog  ? 

d.  In  what  region  (anterior  or  posterior)  of  the  roof 

of  the  mouth  cavity  are  the  inner  openings  of 
the  nostrils  located? 

3.  (Demonstration.)     Just  back  of  the  tongue  there  is 

a  narrow  opening  that  leads  into  the  windpipe 
(trachea).  This  opening  is  called  the  glottis. 

a.   Locate  the  glottis. 

6.  Does  the  glottis  extend  lengthwise  or  crosswise 
of  the  mouth  cavity? 

c.    Into  what  does  the  glottis  open? 

4.  Examine  a  dissected  frog  prepared  in  such  a  way  as 

to  show  the  lungs. 
101 


102  ANIMAL  BIOLOGY 

a.  State  the  location  of  the  lungs  with  reference  to 

the  head  and  the  cavity  of  the  trunk. 

b.  Describe  the  appearance  of  the  lungs. 

c.  Insert  the  end  of   a  glass  tube,  that  has  been 

drawn  out  to  a  small  diameter,  into  the  glottis 
opening  and  blow  air  into  the  lungs.  Describe 
what  you  have  done  and  state  the  result. 
5.  Name  in  order  the  openings,  the  cavity,  and  the  tube 
through  which  the  air  must  pags  in  order  to 
reach  the  lungs. 

C.  Breathing  movements. 

1.  Place  a  frog  in  a  glass  jar  with  an  inch  or  two  of  water 

and  watch  the  action  of  the  floor  of  the  mouth. 
This  is  one  of  the  breathing  movements.  De- 
scribe this  breathing  movement  of  the  frog. 

2.  There  are  two  breathing  movements  of  the  sides  of 

the  trunk,  one  a  very  active  inward  and  out- 
ward movement,  and  the  other  a  very  slight 
inward  and  outward  movement.  When  you 
have  seen  these  two  kinds  of  movements  of 
the  sides,  describe  them  and  state  which  kind 
occurs  the  more  frequently. 

D.  How  the  frog  exhales. 

1.  What  effect  will  the  active  inward  movement  of  the 

sides  have  upon  — 

a.  The  size  of  the  body  cavity  ? 

b.  The  size  of  the  lungs  ? 

c.  The  pressure  of  the  air  in  the  lungs  ? 

2.  When  the  sides  of  the  trunk  move  actively  inward, 

will  the  air  move  into  the  lungs  or  out  ?     Why  ? 

3.  Through  what  passages  will  the  air  go  from  the  lungs 

to  the  outside  of  the  frog  ? 

E.  How  the  frog  inhales.  * 

1.   When  the  floor  of  the  mouth  moves  downward  — 
a.   Will  the  size  of  the  mouth  cavity  be  made  larger 
or  smaller  ? 


FROGS  AND   THEIR   RELATIVES  103 

b.    If  the  nostrils  are  now  open  will  the  air  move  into 

the  mouth  cavity  or  out?     Why? 
2.   When  the  floor  of  the  mouth  is  raised  — 

a.  Will  the  size  of  the  mouth  cavity  be  increased  or 

decreased  ? 

b.  Will  the  pressure  of  the  air  in  the  mouth  cavity 

be  increased  or  decreased  ? 

c.  If  both  the  nostrils  and  the  glottis  are  now  open, 

in  what  directions  will  air  be  forced  ? 

d.  What  causes  the  slight  outward  movements  of 

the  sides  of  the  trunk  in  the  region  of  the 
lungs  ? 

F.  How  the  lungs  are  fitted  for  breathing  organs.     (Suggested 

as  home  work.) 

When  the  lungs  are  inflated  (see  B,  4  above) 
they  look  like  bags  (Fig.  80).  The  lungs  are 
hollow,  and  their  walls  are  composed  of  thin 
material.  In  these  membranous  walls  are  thin- 
walled  blood  vessels  known  as  capillaries.  The 
heart  forces  blood  that  has  come  from  the 
body  into  these  capillaries  of  the  lungs,  and 
then  back  to  the  heart.  Bearing  in  mind  that 
respiration  in  animals  is  essentially  the  same 
as  in  plants  (P.  B.,  82)  - 

1.  State  what  waste  substance  the  blood  brings  to  the 

lungs  to  be  given  off  from  the  capillaries. 

2.  What  gas  will  the  blood  in  the  capillaries  take  up 

from  the  air  in  the  lungs  ? 

3.  How  are  the  walls  of  the  lungs  and  of  the  capillaries 

of  the  lungs  fitted  by  structure  to  make  this 
interchange  of  gases  possible? 

G.  Food-getting. 

To  the  Teacher.  —  Select  a  number  of  as  large  pre- 
served or  freshly  killed  frogs  as  you  can  get.  Open 
the  jaws  as  far  as  possible  and  keep  them  in  this 
position  by  means  of  small  pieces  of  wood. 


104  ANIMAL  BIOLOGY 

1.  Seize  the  posterior  or  hind  end  of  the  tongue  and  pull 

it  forward. 
a.   Tell  what  you  have  done  and  state  which  end  of 

the  tongue  is  attached  to  the  floor  of  the  mouth. 
6.    Describe  the  shape  of  the  tip  end  of  the  tongue. 

2.  The  living  frog  can  extend  its  tongue  much  farther 

than  you  have  been  able  to  do  in  the  case  of 
the  preserved  frog,  and  in  the  living  frog  the 
tongue  is  covered  with  a  very  sticky  substance. 
The  tongue  is  used  to  catch  insects  at  some 
distance  from  the  animal  (Fig.  79).  Tell  how 
you  think  the  frog  could  use  its  tongue  to  catch 
insects  and  get  them  into  its  mouth.1 

3.  Look  for  teeth  on  the  jaws  of  a  skeleton  of  a  frog, 

or  if  you  cannot  obtain  a  skeleton,  rub  the  finger 
over  the  jaws  of  a  preserved  specimen. 

a.  Which  of  the  jaws  has  teeth? 

b.  Describe  the  location  of  the  teeth  on  the  jaw. 

c.  State  the  shape  and  size  of  the  jaw  teeth. 

d.  What  is  the  probable  use  of  the  jaw  teeth? 

4.  (Optional.)     Look  on  the  roof  of  the  mouth  for  two  rela- 

tively large  palate  teeth.     Rub  the  fingers  over  the 

surface  of  the  palate  teeth. 
a.  Tell  what  you  have  done. 

6.   What  have  you  found  out  about  the  palate  teeth? 
c.  What  is  the  probable  use  of  the  palate  teeth  ? 

H.   How  a  frog  swallows. 

1.  Gently  touch  the  eyes  of  a  living  frog  until  it  draws 

them  into  the  head.  Tell  what  you  have  done 
and  observed. 

2.  Look  at  the  roof  of  the  mouth  of  a  preserved  speci- 

men while  you  push  the  eyes  into  the  head. 
Tell  what  you  have  done  and  describe  the  effect 
produced  in  the  roof  of  the  mouth. 

3.  How  will  the  act  of  pushing  the  eyes  into  the  head 

be  useful  to  a  frog  in  swallowing  ? l 

*If  possible  live  frogs  should  be  fed  on  meal  worms,  or  other 
insects,  and  the  feeding  movements  observed. 


FROGS  AND   THEIR   RELATIVES  105 

I.    (Optional.)     Sketch  of  the  mouth  cavity. 

1.  Open  wide  the  mouth  of  a  large  frog  and  make  a  sketch  to 

show  the  shape  of  the  mouth  cavity  twice  the  natu- 
ral size,  and  the  shape  and  thickness  of  the  upper 
and  lower  jaws. 

2.  Draw  the  following  parts  to  show  their  location,  size,  and 

shape:  jaw  teeth,  palate  teeth,  tongue,  glottis, 
nostril  openings,  swellings  caused  by  the  eyes. 

3.  Farthest  back  in  the  throat  find  an  opening  that  extends 

crosswise.  It  is  the  opening  into  the  gullet  and  is 
just  behind  the  glottis.  Push  the  handle  of  the 
forceps  into  this  opening  and  draw  it  (in  your 
sketch)  partly  opened. 

4.  Label  upper  jaw,  lower  jaw,  jaw  teeth,  palate  teeth,  tongue, 

glottis,  opening  of  gullet,  nostril  openings,  swellings 
caused  by  eyes. 

J.    Structure  of  arms  and  leg 

Place  a  frog  in  a  glass  jar  at  least  half  full 
of  water  to  cause  the  animal  to  extend  the  hind 
legs. 

1.  Make  a  sketch  (natural  size)  of  an  arm  to  show  the 

shape  and  size  of  the  following  parts :  upper 
arm,  elbow,  forearm,  hand,  number  of  fingers. 
Label  each  part. 

2.  Draw  one  of  the  legs  (natural  size)  to  show  the  follow- 

ing parts:  thigh  (next  the  body),  knee,  shank, 
ankle  (elongated  region  above  foot),  foot,  toes, 
web  between  toes.  Label  each  part. 

K.  How  a  frog  swims. 

Place  an  active  frog  in  a  sink  or  other 
receptacle  large  enough  to  afford  it  room 
to  swim.  The  water  should  be  deep  enough 
so  that  the  frog  will  not  strike  the  bottom  with 
the  legs.  Get  the  frog  to  swim  the  full  length  of 


106  .        ANIMAL  BIOLOGY 

the  receptacle  as  many  times  as  may  be  neces- 
sary to  answer  the  following  :  — 

1.  Tell  what  you  have  done. 

2.  Describe  the  movements  of  the  hind  legs  in  swimming. 

3.  In  which  of  these  movements  are  the  toes  spread  out  ? 

4.  In  which  of  these  movements,  therefore,  can  the  frog 

get  the  best  hold  upon  the  water  ? 

5.  In  which  direction  must  the  frog  push  the  harder  in 

order  to  move  in  the  direction  that  it  does? 

6.  In  what  respects  are  the  posterior  appendages  well 

fitted  for  swimming? 

7.  In  what  respects  are  the  anterior  appendages  not  as 

well  fitted  as  the  legs  for  swimming  ? 

L.    How  a  frog  jumps. 

Place  a  frog  where  there  is  plenty  of  room, 
and  get  it  to  jump  as  many  times  as  necessary 
to  answer  the  following  :  — 

1.  Tell  what  you  have  done. 

2.  Describe  the  position  of  the  parts  of  the  legs  just  before 

the  frog  jumps. 

3.  Describe  the  two  movements  made  by  the  parts  of 

the  leg  in  the  act  of  jumping  and  when  about 
to  land.  » 

4.  In  which  of  these  two  movements  must  the  frog  use 

the  greater  force  ? 

5.  Which  movement,   therefore,   throws  the  frog  into 

the  air?. 

6.  In  what  respects  are  the  legs  better  adapted  for  jump- 

ing than  the  arms? 

N.  Internal  organs. 

To  the  Teacher.  —  Put  into  a  covered  jar  enough  frogs 
to  supply  each  two  students  with  a  specimen.  Put 
into  the  jar  some  ether,  or  better,  saturate  a  small 
sponge  with  the  ether  and  place  it  in  the  jar.  When 
the  animals  are  dead,  dissect  them  as  follows  :  lift 
up  the  skin  of  the  ventral  wall  of  the  abdomen  with 


FROGS  AND   THEIR  RELATIVES  107 

the  forceps  ;  carefully  insert  the  point  of  the  scissors 
near  the  posterior  end  of  the  trunk,  and  carefully  cut 
forward  on  one  side  of  the  body  as  far  as  the  tip  of 
the  head,  and  back  on  the  other  side  of  the  trunk, 
until  the  skin  is  completely  removed  from  the  ventral 
surface.  In  a  similar  manner  remove  the  muscular 
wall  that  covers  the  trunk,  being  careful  not  to  injure 
the  internal  organs.  If  time  allows,  remove  also  the 
skin  from  one  leg ;  call  attention  to  the  thinness  of 
the  skin  and  to  the  underlying  blood  vessels  ;  show  the 
characteristics  and  action  of  the  leg  muscles. 

If  the  specimen  is  a  female,  remove  nearly  all  the  eggs 
and  throw  them  away.  Insert  a  blowpipe  in  the  glot- 
tis and  partly  inflate  the  lungs.  Wash  the  specimens 
thoroughly  to  remove  all  traces  of  blood  and  cover 
them  with  water  in  a  dissecting  pan. 

If  the  specimens  are  needed  on  successive  days,  they 
should  be  wrapped  in  a  wet  cloth  immediately  after 
the  class  work  of  each  day  and  kept  in  a  cold  place. 
Use  only  specimens  that  are  fresh. 

1.  Make   an   outline   drawing,   natural   size    (or  twice 

natural  size  if  the  frogs  are  small),  of  the  ventral 
view  of  the  head  and  trunk  regions  of  a  dissected 
specimen,  together  with  the  base  of  each  of  the 
four  appendages,  and  dfaw  nothing  else  until 
directed  to  do  so. 

2.  The  heart  is  a  cone-shaped  body  midway  between  the 

arms.  Draw  the  heart  to  show  its  position, 
shape,  and  relative  size. 

3.  On  either  side  of  the  heart  are  the  lungs.     Stretch 

one  of  them  a  little  by  pulling  on  it ;  then  letting 

„  li  SO. 

a.  State  whether  or  not  the  lungs  are  elastic.     Are 

they  hollow  or  solid?  Of  what  advantage  are 
these  two  characteristics  of  structure  ? 

b.  What  is  the  color  of  the  lungs?     State  whether 

or  not  you  find  tiny  blood  vessels  on  the  sur- 
face. 


108  ANIMAL   BIOLOGY 

c.    Draw  the  lungs  in  position  to  show  their  situation, 
size,  and  shape. 

4.  On  the  frog's  right  side,  and  behind  the  heart  and 

lungs  is  the  reddish,  several-lobed  liver.  Lay 
the  liver  over  to  one  side  and  find  between  the 
lobes  on  the  underside  a  thin-walled,  green  sac, 
the  bile  sac  (or  gall  bladder).  Sketch  in  your 
drawing  the  liver  to  show  it  in  this  position 
together  with  the  gall  bladder. 

5.  On  the  frog's  left  side  and  under  the  liver  in  its 

natural  position  is  a  whitish,  oblong  body, 
which  narrows  at  its  hinder  end.  This  body  is 
the  stomach.  Push  the  handle  of  the  dissecting 
needle  down  the  gullet  into  the  stomach. 

a.  Tell  what  you  have  just  done. 

b.  What  organ  does  the  handle  enter? 

c.  Push  the  stomach  to  the  frog's  left  and  draw  it 

in  this  position  to  show  its  shape  and  relative 
size. 

6.  Extending  from  the  stomach  is  a  tubular  structure 

of  considerable  length,  the  small  intestine.  At 
the  lower  end  of  the  small  intestine  the  tube 
becomes  larger  and  then  disappears  between 
the  two  thighs.  This  last  part  of  the  tube  is 
called  the  cloaca  or  large  intestine. 
Draw  the  small  and  large  intestines. 

7.  Between  the  stomach  and  the  first  loop  of  the  small 

intestine  is    a  thin    pink  body,  the  pancreas, 
which  is  a  very  important  digestive  gland. 
Draw  the  pancreas. 

8.  Label  heart,  lungs,  liver,  stomach,  small   intestine, 

large  intestine,  bile  sac,  pancreas. 

9.  Push  the  small  intestine  to  one  side  and  find  two  red 

bodies  on  either  side  of  the  spinal  column. 
These  bodies  are  the  kidneys.  The  kidneys 
remove  the  nitrogenous  waste  (urea}  from  the 
blood. 

Make  a  sketch  of  the  kidneys  twice  the  natural 
size. 


FROGS  AND   THEIR  RELATIVES 


109 


82.  Habits  of  frogs.  —  There  are  many  kinds  of  frogs, 
differing  from  one  another  considerably  in  size  and  color ;  but 
all  frogs  live  in  places  where  water  is  more  or  less  abundant. 
Frogs  are  often  found  either  on  the  banks  of  ponds  and 
streams,  or  floating  on  the  surface  of  the  water  with  only  the 
tip  of  the  nose  above  water  (Fig.  78).  In  color  they  usually 
resemble  their  surroundings  rather  closely,  and  so  secure 
a  certain  degree  of  protection  from  fishes,  snakes,  birds,  and 


FIG.  78.  —  Frogs  in  their  habitat.  Four  frogs  are  shown  ;  in  the  middle  of 
the  picture  a  black  snake  is  preparing  to  seize  the  frog.  (Part  of 
an  exhibit  at  American  Museum  of  Natural  History.) 


man,  which  are  their  more  common  enemies.  When  pur- 
sued, they  quickly  disappear  beneath  the  water  and  often 
bury  themselves  in  the  mud  at  the  bottom  until  the  need  of 
air  compels  them  to  return  to  the  surface.  Late  in  the 
autumn  they  burrow  in  the  mud  and  remain  there  until  the 
following  spring.  The  more  or  less  pointed  snout  of  the  frog, 
its  slippery  skin,  its  long,  muscular  legs,  and  its  webbed  feet 
all  adapt  the  animal  for  rapid  swimming  through  the  water. 


110 


ANIMAL  BIOLOGY 


83.  Food,  food-getting,  and  digestion.  —  Frogs  feed  upon 
insects,  fish,  and  other  frogs,  and  even  birds  have  been  found 
in  their  stomachs.      Insects  are  caught  by  the  aid  of  the 
slimy  tongue,  the  tip  of  which  can  be  quickly  thrust  out  of 
the  mouth  and  then  drawn  back  again  with  the  insect  adher- 
ing to  it  (Fig.  79).    The  tiny  teeth  that  are  found  on  the  upper 

jaw  and  the  two  large  teeth  in  the  roof  of 
the  mouth  are  useful  only  in  preventing 
the  escape  of  the  prey  from  the  mouth. 
Hence  the  food  is  swallowed  without 
being  chewed,  and  after  passing  down 
the  short  gullet  it  enters  the  tubular 
stomach  (Fig.  80),  where  it  is  partially 
digested  by  ferments  (P.  B.,  53)  secreted 
by  certain  cells  found  in  the  lining  of 
this  organ. 

When  the  food  leaves  the  stomach, 
it  enters  the  coiled  small  intestine  where 
the  process  of  digestion  is  continued  by 
the  bile  secreted  in  the  liver  and  the 
pancreatic  juice  prepared  in  the  pan- 
creas.1 As  the  digested  food  slowly  moves 
along  the  small  intestine,  it  is  absorbed 
by  the  capillaries  (84)  in  the  walls  of  this  tube  and  so  may 
be  carried  by  the  blood  to  the  various  cells  of  which  the 
body  is  composed.  Digestion  not  only  prepares  the  food 
for  absorption,  but  as  in  plants  (P.  B.,  51)  or  in  the  fish 
(98),  makes  it  ready  to  be  used  in  the  cells  either  for  growth 
and  repair  or  for  the  production  of  energy. 

84.  Blood    and    circulation.  —  The    blood    of    the    frog, 
when  examined  under  the  microscope,   is  seen  to  consist 

^oth  of  these  digestive  fluids  are  carried  to  the  intestine  by 
ducts. 


FIG.  79.  — The  method 
by  which  a  frog  se- 
cures insects. 


FROGS  AND   THEIR   RELATIVES 


111 


of  two  kinds  of  cells  (the  red  and  white  corpuscles)  which 
are  floating  in  a  liquid  known  as  plasma.  The  plasma  con- 
sists largely  of  water  and  the  digested  foods  that  have  been 
absorbed  from  the  alimentary  canal  (83). 

As  in  the  fish,  the  circulatory  system  consists  of  the  heart 
and  three  kinds  of  blood  vessels ;  namely,  arteries,  veins,  and 


FIG.  80.  —  Internal  organs  of  the  frog. 

capillaries.  The  heart  is  located  in  the  body  cavity  just  back 
of  the  head  and  consists  of  two  auricles  and  a  ventricle 
(Fig.  81),  instead  of  a  single  auricle  and  ventricle  as  in  the  fish 
(Fig.  100).  As  might  be  expected,  this  makes  necessary  other 
differences  in  the  circulatory  system  of  the  frog.  In  the  fish 
we  shall  see  that  there  is  only  one  stream  of  blood  flowing  into 
the  heart,  while  in  the  frog  there  are  two.  One  stream 
enters  the  heart  from  the  various  organs  of  the  body  which 
the  blood  has  supplied  with  food  and  oxygen,  and  from  which 
the  blood  has  received  carbon  dioxid.  The  second  blood 


112 


\ 
ANIMAL  BIOLOGY 


stream  comes  from  the  lungs  where  the  blood  has  given  off 
the  carbon  dioxid  and  received  a  fresh  supply  of  oxygen. 
The  right  auricle  receives  the  blood  brought  from  the  body 
in  three  large  veins,  while  two  small  veins  carry  into  the  left 
auricle  the  blood  from  the  lungs. 


Arterytoleft 
\sjuny  eutftsfait 


Artery  tp  left  arm 
'.'-- lettauric/e 
fe/itric/e 


— -ieftlurtg 
-Dorsa/aorta 


Arteries  fy 
kidneys 


''^^"-Arter/'es  to  legs 

A 

FIG.  81.  —  Arteries  in  the  circulation  of  the  frog. 

The  blood  from  both  auricles  now  flows  into  the  single 
ventricle,  which  then  contracts  and  pumps  the  blood  into  a, 
large  artery.  Certain  branches  carry  the  blood  having  the 
larger  amounts  of  oxygen  (i.e.  the  blood  from  the  lungs) 
to  the  head,  trunk,  legs,  and  other  organs  of  the  body,  while 
other  branches  carry  the  blood  just  received  from  the  body, 


FROGS  AND   THEIR  RELATIVES 


113 


with  its  larger  amount  of  carbon  dioxid,  to  the  lungs  and  the 
skin. 

In  the  capillaries  which  connect  the  arteries  and  veins  in 
every  part  of  the  body  (Fig.  82)  all  the  changes  in  the  com- 
position of  the  blood  take  place,  since  their  thin  walls  per- 
mit the  food  materials  and  oxygen  to  enter  the  cells  and  the 
wastes  from  the  cells  to  enter  the  blood.1  The  capillaries 
in  the  lungs  likewise  permit  the  interchange  of  oxygen  and 
carbon  dioxid. 


FIG.  82.  —  Network  of  cap- 
illaries connecting  an  ar- 
tery and  a  vein. 


FIG.  83.  —  Capillaries  in  web  of 
frog's  foot. 


85.  Respiration  and  the  liberation  of  energy.  —  The  walls 
of  the  frog's  lungs  contain  a  network  of  capillaries,  and  in 
these  thin-walled  tubes  the  red  corpuscles  absorb  the  oxygen 
that  is  forced  into  these  sacs  by  the  upward  movement  of 
the  floor  of  the  mouth.  As  we  have  seen,  the  blood  with  a 
fresh  supply  of  oxygen  flows  from  capillaries  of  the  lungs  into 

1  A  tadpole's  tail  is  excellent  for  demonstrating  the  blood  current. 
Wrap  a  tadpole  in  wet  cloth  or  cotton  and  support  it  so  that  the  tail 
can  be  placed  between  two  glass  slides  on  the  stage  of  the  micro- 
scope. The  space  between  the  two  slides  should  be  kept  filled 
with  water.  The  movement  of  the  corpuscles  through  the  margin 
of  the  tail  should  be  examined  with  the  low  power  of  the  micro- 
scope (Fig.  83). 


114  ANIMAL  BIOLOGY 

veins  and  so  finally  into  the  left  auricle  and  thence  into  the 
ventricle.  Here  it  tends  to  become  somewhat  mixed  with 
the  blood  from  the  right  auricle  which  has  just  returned  from 
the  body.  However,  the  structure  of  the  heart  and  the  ar- 
teries is  such  that  the  blood  that  has  come  from  the  lungs  with 
a  larger  supply  of  oxygen  is  sent  out  by  arteries  to  all  parts 
of  the  body. 

In  the  capillaries  the  oxygen  is  absorbed  by  the  cells. 
Oxidation  of  the  food  and  protoplasm  takes  place  and  en- 
ergy is  thereby  released,  which  enables  the  frog  to  carry  on 
locomotion,  secure  its  food,  and  perform  all  its  destined  tasks. 
The  carbon  dioxid  and  other  wastes  produced  by  oxidation 
pass  through  the  capillary  walls  into  the  blood  and,  as  we 
have  seen,  are  carried  back  to  the  heart  and  then  to  the  lungs, 
where  carbon  dioxid  is  excreted.  Other  wastes  are  excreted 
by  the  kidneys. 

The  skin  of  the  frog  is  likewise  permeated  by  a  network 
of  capillaries  so  that  it  acts  ks  do  the  gills  of  fishes  in  ab- 
sorbing oxygen  from  the  water  and  in  giving  off  carbon 
dioxid.  While  the  frog  is  buried  in  the  mud  during  the  winter 
it  breathes  entirely  through  the  skin.  So  much  does  the 
frog  depend  on  the  skin  as  a  breathing  organ  that  even  in 
summer,  if  the  skin  becomes  dry  so  that  air  cannot  be  ab- 
sorbed, the  frog  dies. 

86.  Reproduction  and  life  history.  —  In  the  animals 
studied  thus  far  we  have  found  special  organs  devoted  to  the 
process  of  reproduction,  namely,  ovaries  for  egg  production 
in  the  female  and  in  the  male  spermaries  that  form  the 
sperm-cells.  Before  the  egg-cells  can  develop  into  embryos 
each  must  be  fertilized  by  a  sperm-cell.  All  the  facts  we 
have  just  stated  apply  equally  well  to  the  frog. 

Frogs'  eggs  are  deposited  in  springtime  in  masses  that 


FROGS  AND   THEIR  RELATIVES 


115 


C,     egg     con- 

A,  eggs  before      B,  eggs  after  they       taining  young         D,  young  tadpoles  attaching 
they  are  laid  are  laid  tadpole  themselves  to  a  plant 


t 


E,  young  tadpole  with  ex-      F,  young  tadpole  with 

ternal  gills  internal  gills  G,  young  tadpole  with  hind  legs 


H,  tadpole  with  webbed 

feet  J>  tadpole  with  legs  and  arms 

FIG.  84.  —  Life  history  of  frog. 


young  frog 


A,  one-ce'lled  stage       B,  two-celled  stage       C,  four-celled  stage      D,  eight-celled  stage 


,  sixteen-celled 
stage 


F,  thirty-two 
celled  stage 


G,   sixty-four 
celled  stage 


FIG.  85.  —  Cell  division  in  a  frog's  egg. 


H,  many-celled 
stage 


116  ANIMAL  BIOLOGY 

float  on  the  surface  of  the  water1  (Fig.  84,  B).  Each  fertil- 
ized egg  is  a  small  sphere,  black  on  its  upper  surface  and  white 
beneath,  and  inclosed  in  a  gelatinous  covering.  The 
warmth  of  the  sun  causes  the  one-celled  egg  to  divide  verti- 
cally in  half  to  form  the  two-celled  stage  (Fig.  85,  B)  and  the 
process  of  division  continues  until  the  egg  consists  of  many 
cells  (Fig.  85,  H).  Food  for  the  development  of  the  embryo 
is  stored  in  the  egg. 

The  many  cells  of  the  egg  gradually  become  different  in 
character  and  so  form  the  various  organs  of  the  embryo 

(Fig.  86).  Soon  after  hatching, 
the  young  of  the  frog,  known  as 
tadpoles,  secure  their  food  by 
sucking  in  tiny  water  plants 
found  on  the  surface  of  plants 

FIG.  86.  —  Embryo  of  frog.  ,  /T,.       _.     _,        „,     , 

and  stones  (Fig.  84,  D).  Tad- 
poles resemble  fishes  in  having  gills  for  breathing,  a  heart 
with  two  chambers  instead  of  three,  and  a  tail  for  locomotion. 
At  first  the  gills  are  on  the  outside  of  the  body  (Fig.  84,  E) ,  but 
later  four  pairs  of  internal  gills  are  formed,  and  the  external 
gills  are  absorbed.  The  animal  increases  in  size,  the  hind  legs 
appear,  and  the  arms  are  formed  beneath  the  skin.  Meanwhile 
the  lungs  are  being  developed,  the  heart  becomes  three  cham- 
bered, the  legs  grow  larger,  arms  appear,  and  finally  the 
gills  and  the  tail  are  completely  absorbed.  The  tadpole 
now  leaves  the  water,  since  it  is  an  air-breathing  animal. 
This  succession  of  changes  after  hatching  from  the  egg  is 
known  as  a  metamorphosis. 

87.    Relatives  of  the  frog.  —  Much  like  the  frog  in  structure  and 
life  history  is  the  common  garden  toad.     Toads,  however,  in  their 

1  If  possible  eggs  in  different  stages  of  segmentation  should  be  se- 
cured, preserved  in  5  per  cent  formalin,  and  used  for  demonstration. 


FROGS  AND   THEIR  RELATIVES 


117 


adult  stage  cover  themselves  more  or  less  with  dirt  in  the  daytime, 
and  come  out  at  night  to  feed  upon  insects,  which  constitute  their  sole 
food.  Instead  of  having  a  smooth,  slimy  skin,  as  does  the  frog, 
a  toad's  skin  (Fig.  87)  is  dry  and  covered  with  elevations  com- 
monly known  as  "  warts."  These  elevations  contain  cells  which 
secrete  an  irritating  substance  that  protects  the  toad  from  animals 


FIG.  87.  —  The  toad.    Note  its  resemblance  to  its  surroundings,  whereby 
it  is  likely  to  be  protected. 

that  would  prey  upon  it.  There  is  no  foundation,  however,  for 
the  popular  notion  that  the  warts  of  human  beings  are  ever  caused 
either  by  toads  or  frogs. 

In  springtime  toads  seek  the  water  in  which  to  breed.  The  eggs, 
covered  with  a  gelatinous  substance  are  laid  in  long  strings  instead 
of  in  masses,  as  was  the  case  with  frogs.  The  development  and  life 


118  ANIMAL  BIOLOGY 

history  of  the  toad  is  much  the  same  as  in  the  case  of  the  frog.  As 
soon  as  metamorphosis  is  complete,  the  little  toads  leave  the  water 
and  often  are  found  considerable  distances  away  from  water. 

Less  like  the  frog,  at  least  in  its  adult  stage,  are  the  salamanders 
and  newts  (Fig.  88).      These  are  found  in  damp  places  or  in 


FIG.  88.  —  The  newt. 

water  and  are  often  called  "lizards,"  by  those  who  do  not  know 
that  a  lizard  has  scales,  claws  on  its  feet,  and  breathes  throughout 
its  life  by  means  of  lungs.  Some  of  the  relatives  of  the  frog,  even 
after  they  have  developed  lungs,  retain  gills  throughout  their 
life  (Fig.  89). 


FIG.  89.  —  A  mature  amphibian  (Necturus)  with  external  gills. 

Because  of  the  ability  of  the  animals  described  in  this  chapter  to 
live  both  on  the  land  and  in  the  water,  they  are  called  the  amphibia, 
from  Greek  amphi  =  both  +  bios  =  life. 

88.  Economic  importance  of  the  amphibia.  —  None  of 
the  amphibia,  so  far  as  is  known,  are  harmful  to  man.  On 
the  contrary,  all  of  them  are  more  or  less  useful  because  of  the 
insects  that  they  devour.  This  is  especially  true  of  the  garden 
toad.  It  has  been  estimated  by  one  author  that  a  toad  in 
a  garden  is  worth  nearly  twenty  dollars  a  year  on  account 
of  the  cutworms  and  other  injurious  insects  that  it  destroys. 
"  In  France  the  gardeners  even  buy  toads  to  aid  them  in 


FROGS  AND   THEIR   RELATIVES  119 

keeping  obnoxious  insects  under  control."-  —  HEGNER'S  "  Col- 
lege Zoology." 

Frogs,  in  addition  to  their  value  as  insect  destroyers,  are 
also  of  some  value  to  man  as  food.  It  is  said  that  in  the 
United  States  about  $50,000  is  obtained  annually  by  the  frog 
hunters  for  their  catch,  and  frog  farms  are  now  profitably 
maintained  in  several  states.  Frogs  are  also  used  as  fish  bait. 


CHAPTER  IV 
FISHES 

89.  What  is  a  fish  ?  —  "  A  fish  is  a  backboned  animal  which 
lives  in  the  water  and  cannot  ever  live  very  long  anywhere 
else.  Its  ancestors  have  always  dwelt  in  water,  and  likely 
its  descendants  will  forever  follow  their  example.  So,  as  the 


FIG.  90.— Yellow  perch. 

water  is  a  region  very  different  from  the  fields  or  the  woods, 
a  fish  in  form  and  structure  must  be  quite  unlike  all  the 
beasts  and  birds  that  walk  or  creep  or  fly  above  ground, 
breathing  air,  and  being  fitted  to  live  in  it.  There  are  a 

120 


FISHES  121 

great  many  kinds  of  animals  called  fishes,  but  in  this  all  of 
them  agree :  all  have  some  sort  of  a  backbone,  all  of  them 
breathe  their  life  long  by  means  of  gills,  and  none  have 
fingers  or  toes  with  which  to  creep  about  on  land." 1 

90.  The  regions  and  appendages   of   a  yellow  perch.  — 

Study  Figure  90  and  notice  that  the  body  of  the  yellow  perch 
is  divided  into  three  regions ;  namely,  head,  trunk,  and  tail. 
Unlike  the  body  of  many  animals,  no  neck  is  present,  and  the 
head,  therefore,  is  joined  directly  to  the  trunk.  The  line 
of  union  of  head  and  trunk  is  the  posterior 2  margin  of 
movable  flaps,  called  the  gill  covers,  on  the  sides  of  the  head. 
Just  behind  or  posterior  to  the  gill  cover  on  each  side  of  the 
trunk  of  the  fish  is  a  paddle-like  organ  called  the  pectoral  fin. 
On  the  ventral  surface,  below  the  pectoral  fins,  is  a  second 
pair  which  are  known  as  the  pelvic  fins.  The  pectoral  and 
pelvic  fins  are  together  known  as  the  paired  fins  of  the  fish. 
Besides  these  this  animal  has  several  unpaired  fins,  which 
we  shall  now  locate.  On  the  dorsal  surface  notice  two 
dorsal  fins,  one  behind  the  other,  which  project  upward. 
Below  the  posterior  dorsal  fin,  on  the  ventral  surface,  is 
another  single  fin  called  the  anal  fin.  The  tail  region  is 
considered  to  begin  just  in  front  of  the  anal  fin,  since  in  the 
fish  the  body  cavity  that  contains  the  important  organs  of 
digestion,  circulation,  and  reproduction  ends  at  this  point 
(Fig.  98).  The  anal  fin,  therefore,  and  also  most  of  the 
posterior  dorsal  fin,  are  attached  to  the  tail  region.  At  the 
posterior  end  of  this  third  region  is  the  broad  forked  tail 
fin. 

91.  Regions  and  appendages  of  a  goldfish.  —  Laboratory 
study. 

1  Jordan's  "Guide  ta  the  Study  of  Fishes,"  Vol.  I,  p.  3. 

2  The  meaning  of  each  of  these  terms  is  explained  in  6. 


122 


ANIMAL  BIOLOGY 


Materials:  A  living  goldfish  in  a  battery  jar  for  each  two 
students.  Goldfish  may  be  kept  indefinitely  in  a  glass  jar  with 
green  water  plants ;  the  latter  supply  the  fish  with  food  and  oxygen. 
Perch,  and  if  possible  the  heads  of  large  fishes  like  the  cod,  should  be 
obtained,  preserved  in  formalin  (5  per  cent),  and  then  thoroughly 
washed  in  running  water  for  twenty-four  hours  before  they  are  used ; 
material  treated  in  this  way  loses  its  fishy  smell,  and  may  be  kept  in 
the  formalin  solution  year  after  year.  A  fish  skeleton  is  also  needed 
for  demonstration.  The  Jung  charts  of  the  external  and  internal 
structure  of  the  perch  are  useful. 

Observe  a  living  goldfish  and  compare  it  with  Figure  90. 

1.  Name  the  regions  of  its  body  and  state,  with  reference  to 

gill  cover  and  fins,  where  each  region  begins  and  ends. 

2.  Name  and  locate  all  the  organs  you  find  on  the  head. 

3.  What  paired  and  what  unpaired  fins  are  found  on  the 

trunk?     Using  the  terms  anterior,   posterior,   dorsal, 
ventral,  median,  and  lateral,  locate  each  of  these  fins. 

4.  Name  and  locate  the  fins  attached  to  the  tail  region  of 

the  body. 

5.  Make   an   outline   sketch   about  five 

inches  long  of  the  side  view  of  a 
living  goldfish  to  show  the  shape 
and  relative  size  of  the  three  re- 
gions, the  position  and  shape  of  the 
organs  of  the  head  and  of  the 
various  kinds  of  fins.  Label  the 
regions  and  the  organs  that  you 
have  drawn,  in  a  manner  similar  to 
Figure  90. 

92.  Some  differences  in  the  form  of  fishes. 
—  One  can  usually  tell  whether  or  not  an 
animal  is  a  fish;  but  in  some  cases  this  is  FIG.  91.  —  Seahorse. 


FISHES 


123 


extremely  difficult.     Who  would  think,  for  instance,  that  such  ani- 
mals as  the  sea  horse  (Fig.  91)  and  the  pipefish  (Fig.  92)  would  be 


FIG.  92.  —  Pipefish. 


classed  with  the  perch  and  goldfish  ? 
careful  study  has  shown  that  these 
teristics  mentioned  in  89. 

dorsal  fin 


Yet  such  is  the  case,  since 
forms  have  all  the  charac- 


anal fin 
FIG.  93.  —  Flounder. 


pelvic  fin 


It  is  evident  that  the  goldfish  and  perch  have  bodies  that  are 
considerably  longer  than  they  are  wide  or  deep,  and  this  is  true  of 
most  of  the  common  fishes.  In  the  group  of  fishes  known  as  the  eels, 


124 


ANIMAL  BIOLOGY 


this  elongation  is  so  marked  that  they  look  more  like  snakes 
than  they  do  like  fishes.  But  the  eels  are  not  the  only  fishes  that 
show  a  striking  development  in  one  dimension.  The  flounders,  for 
example  (Fig.  93),  exhibit  a  notable  growth  in  a  dorso- ventral  direc- 


FIG.  94.  — Stingray. 


(Jordan  and  Evermann. 
Page  &  Co.) 


Courtesy  of  Doubleday, 


tion.  So  far  has  this  been  carried  that  the  fish  is  unable  to  retain 
a  vertical  position,  and  consequently  lies  on  one  of  its  sides.  The 
eyes,  which,  in  very  young  flounders,  are  situated  like  those  of  the 
goldfish,  on  either  side  of  the  head,  by  a  twisting  of  the  bones  of  the 


FIG.  95.  —  Mackerel. 


(Jordan  and  Evermann. 
Page  &  Co.) 


Courtesy  of  Doubleday, 


skull,  both  come  to  lie  on  the  same  side  of  the  head.  Otherwise,  as 
may  be  seen,  one  of  the  eyes  would  rest  on  the  sand  or  mud,  when  the 
animal  is  on  the  sea  bottom.  Fishes  like  the  skates  and  sting  rays 
(Fig.  94)  have  also  a  much  flattened  body,  but  these  animals  have 


FISHES  125 

attained  this  condition  by  growth  from  side  to  side,  instead  of 
dorso-ventrally. 

93.  Some  differences  in  the  fins  of  fishes.  —  We  have  seen  that 
the  goldfish  has  one  dorsal  fin,  the  perch  two,  and  that  both  fishes 
have  a  single  anal  fin.  A  glance  at  Figure  108  will  show  that  the  cod- 
fish has  three  dorsal  fins  and  two  anal  fins.  Dorsal  and  anal  fins 
vary  not  only  in  number,  but  in  extent.  In  some  fishes  they  are 
very  short,  as  in  the  mackerel  (Fig.  95),  while  in  the  flounder  (Fig. 
93)  these  fins  extend  nearly  the  whole  length  of  the  dorsal  and 
ventral  surfaces. 

Most  common  fishes  possess  both  pectoral  and  pelvic  fins,  but 
in  the  eels  (Fig.  96)  the  pelvic  fins  are  entirely  wanting  and  the  pec- 


FIG.  96.  —  Eel.     (Jordan  and  Evermann.    Courtesy  of  Doubleday, 
Page  &  Co.) 

toral  fins  are  very  small.  The  paired  fins  vary  in  position  as  well. 
In  the  perch,  for  example  (Fig.  90)  the  pelvic  fins  are  immediately 
below  the  pectorals,  while  in  the  cod  (Fig.  108)  they  are  anterior 
to  the  pectoral  fins,  and  in  the  salmon  (Fig.  107)  they  are  even  farther 
back  on  the  body  than  in  the  goldfish. 

94.   Adaptations  for  swimming.  —  Laboratory  study. 

1.  Carefully  watch  for  a  time  a  goldfish  when  it  is  swimming 

around  in  a  large  battery  jar  or  aquarium. 

a.  Which  of  the  three  regions  of  the  body  is  principally 

.used  in  pushing  the  animal  forward  ? 

b.  Describe  the 'movements  of  this  body  region. 

2.  WTiich  of  the  paired  fins  are  used  in  swimming?     De- 


126  ANIMAL  BIOLOGY 

scribe  their  movements.  State  whether  or  not  you 
see  the  fish  swim  backward. 

3.  If  the  goldfish  strikes  backward  with  the  fins  against  the 

water,  would  the  fish  tend  to  move  forward  or 
backward  ? 

4.  Since  the  goldfish  moves  the  fins  both  backward  and  for- 

ward in  the  water,  in  which  direction  must  it 
strike  the  harder  and  more  swiftly  if  it  wishes  to 
swim  forward  ? 

5.  (Optional.)     Suppose  the  fish  strikes  backward  harder  with  the 

fins  on  the  right  side  than  it  does  with  those  on  the  left 
side,  how  would  the  direction  of  its  motion  be  affected  ? 

6.  (Optional  demonstration.)     Place  the  largest  goldfish  you  can 

get,  in  a  sink  or  other  large  receptacle  full  of  water.  Get 
the  fish  to  swim  continuously  and  rapidly,  but  not  so 
rapidly  that  the  pupils  are  unable  to  see  the  paired  fins. 

a.  What  have  you   seen  that   leads  you  to  think  that  the 

goldfish  does  not  use  the  paired  fins  in  rapid  swimming  ? 

b.  What  parts  does  the  animal  use  to  drive  itself  rapidly  through 

the  water? 

7.  Why  are  the  broad,  flat  surfaces  of  the  fins  of  advantage 

to  the  fish  in  swimming? 

8.  Study  the  anterior,  dorsal  fin  of  a  perch  or  other  fish. 

Notice  that  it  is  composed  of  stiff  fin  rays  and  of 
thin  connecting  membrane.  Alternately  spread  out 
and  close  the  fin,  and  bend  each  of  the  materials 
of  which  it  is  composed.  Kow  describe  the  struc- 
ture of  this  fin. 

9.  Examine  carefully  each  of  the  fins  of  a  goldfish. 

a.  State  whether  or  not  each  consists  of  fin  rays  and 

connecting  material. 

b.  What  disadvantage  to  a  goldfish  in  swimming  would 

result  from  the  absence  of  the  rays  in  a  fin? 

c.  State  the  relative  difference  in  the  size  of  a  fin  when 

it  is  spread  open  and  when  it  is  closed. 

d.  What  would  be  the  disadvantage  if  the  open  fin  had 

no  connecting  membrane? 


FISHES  127 

95.  The  locomotion  of  fishes.  —  Many  fishes,  like  the 
goldfish  and  perch,  are  able  to  maintain  a  given  position  in 
the  water  while  at  rest.  This  is  made  possible  by  means 
of  an  internal  organ  known  as  the  swim  bladder  (Fig.  98). 
The  swim  bladder  may  be  compressed,  permitting  the  fish 
to  sink,  or  it  may  be  expanded,  causing  the  animal  to  rise. 
Since,  therefore,  the  fish  is  poised  in  a  liquid  medium,  it  is  only 
necessary  to  overcome  the  resistance  of  the  water  about  it  in 
order  to  move  in  any  given  direction.  This  resistance  is  more 
easily  overcome,  first,  because  the  head  is  somewhat  pointed 
like  the  prow  of  a  boat,  secondly,  because  the  overlapping 
scales  point  backward,  and  third,  because  the  whole  body  is 
covered  with  a  slimy  mucus. 

One  who  is  at  all  familiar  with  a  canoe  knows  that  it  is 
impossible  to  propel  it  by  the  use  of  a  slender  rod.  One 
must  have  a  paddle  with  the  lower  end  broad  and  flat  so  that 
sufficient  force  may  be  exerted  against  the  water  to  propel 
the  canoe.  Now,  in  swimming,  the  fins  of  a  fish  act  more  or 
less  like  paddles.  Their  broad,  flat  surfaces  press  against 
such  an  amount  of  water  that  the  fish  is  enabled  to  exert 
enough  force  to  push  its  body  in  any  desired  direction. 

If  one  watches  a  goldfish  swimming  slowly  about  in  an 
aquarium,  one  would  think  that  the  paired  fins,  especially 
the  pectoral  fins,  were  the  important  swimming  organs. 
But  careful  experiments  have  shown  that  this  is  not  the  case. 
When  the  goldfish  has  occasion  to  move  more  rapidly,  the 
paired  fins  are  not  used  at  all,  but  are  pressed  close  to  the 
sides,  the  body  being  driven  through  the  water  by  the 
movement  of  the  tail  and  tail  fin.  The  paired  fins,  to- 
gether with  the  dorsal  and  anal  fins,  seem  to  be  used  prin- 
cipally in  steering  the  fish.  The  energy  necessary  for 
swimming  is  developed  hi  the  powerful  muscles  of  the  tail 
and  trunk. 


128  ANIMAL  BIOLOGY 

I 

96.  Adaptations  for  food  getting.  —  Laboratory  study. 

1.  Open  the  jaws  of  a  fresh  or  of  a  preserved  fish.     (Fish  of 

large  size,  e.g.  cod,  should  be  used  if  possible,  the 
jaws  being  held  wide  open  with  pieces  of  wood.) 
Look  for  teeth  on  the  jaws  and  the  roof  of  the 
mouth. 

a.  State  the  location  of  the  teeth  and  give  some  idea  of 

their  number. 

b.  Rub  the  fingers  gently  back  and  forth  over  the  teeth. 

Do  they  point  backward  or  forward  ?    How  do  you 

know? 
Describe  any  other  characteristics  of  the  teeth. 

c.  Of  what  use  would  the  teeth  be  in  catching  other 

fish  for  food? 

d.  Why  would  the  shape  of  the  teeth  make  them  of  no 

use  in  grinding  food  ? 

2.  Drop  some  fish  food  into  a  jar  containing  living  goldfish.1 

Describe  all  the  movements  that   you   see   the   fish 
make  while  feeding. 

97.  Food  and  food  getting  among  fishes. — Unlike  plants, 
fishes  cannot  make  their  food  from  materials  found  in  the 
water,  air,  and  soil,  but  must  secure  it  ready-made  from 
plants  or  other   animals.     The   goldfish,  for   example,  de- 
pends  largely   on  vegetable  food,  while  the  cod  2   and  the 
perch  for  the  most  part  feed  upon  other  animals  smaller  than 
themselves.     Since  these  fishes  must  catch  and  hold  their 
prey,  their  jaws  are  provided  with  many  sharp  teeth  that 
point  backward,  and  so  prevent  the  escape  of  any  active 

1  If  none  of  the  fish  eat  readily,  this  experiment  should  be  deferred. 
"  The  cod  is  omnivorous,  and  feeds  upon  various  kinds  of  ani- 
mals, including  crustaceans,  molluscs,  and  small  fishes,  and  even 
browses  upon  Irish  moss  and  other  aquatic  vegetation.  All  sorts 
of  things  have  been  found  in  cods'  stomachs,  such  as  scissors,  oil 
cans,  finger  rings,  rocks,  potato  parings,  corn  cobs,  rubber  dolls, 
pieces  of  clothing,  the  heel  of  a  boot,  as  well  as  other  new  and  rare 
specimens  of  mollusks  and  Crustacea."  —  JORDAN  and  EVERMANN, 
"American  Food  and  Game  Fishes." 


FISHES  129 

animal  which  may  have  been  caught.  The  cod,  as  you  may 
have  seen,  has  teeth  in  the  roof  of  the  mouth  and  in  the 
throat  in  addition  to  those  found  on  the  jaws,  thus  making 
more  secure  its  hold  upon  the  unfortunate  denizen  of  the 
deep  that  it  has  seized. 

Certain  fishes  depend  on  minute  forms  of  plants  and  ani- 
mals, and  therefore  some  means  is  needed  by  which  the  water 
taken  in  with  the  food  may  be  gotten  rid  of  while  at  the  same 
time  the  food  is  retained.  Hence,  fishes  are  provided  with 
a  straining  apparatus  which  permits  the  water  to  escape 
when  the  mouth  is  closed,  and  retains  within  the  mouth  the 
minute  forms  of  life  that  it  has  secured.  Of  this  adapta- 
tion for  food  getting,  we  shall  learn  more  in  our  study  of 
the  gills. 

Most  of  the  fishes  that  prey  on  other  animals  secure  their 
victims  by  dint  of  their  speed ;  but  one  form  of  fish,  called 


FIG.  97.  —  Deep  sea  angler. 

the  "deep  sea  angler "  (Fig.  97),  has  upon  the  dorsal  part  of 
the  head  a  bulbous  projection,  the  tip  end  of  which  is  lumi- 
nous. This  bright  light  attracts  other  fishes,  and  when  they 
approach  near  enough,  the  "  angler  "  makes  a  quick  dash, 
closes  its  big  jaws  upon  the  too  curious  individual,  and  so 


130  ANIMAL  BIOLOGY 

secures  food.  But  whatever  a  fish  feeds  upon,  and  however 
it  secures  its  food,  it  is  evident  that  plants  and  other  animals 
must  furnish  the  food  substance  required  to  make  living 
matter,  and  so  provide  for  growth  and  repair  of  the  cells, 
and  also  furnish  the  fuel  needed  to  develop  the  energy  nec- 
essary for  the  various  activities  of  the  fish. 

98.  Digestion  and  digestive  organs.  —  We  have  seen  in 
plants  (P.  B.,  63,  70,  74)  that  digestion  may  take  place  in 
any  living  cell  where  food  is  stored  or  manufactured.  Hence 
plants  have  no  special  part  devoted  to  digestion.  In  fishes 
however,  it  is  quite  different,  since  a  portion  of  the  body, 
known  as  a  digestive  system,  is  devoted  to  preparing  the 
food  for  absorption  and  use.  This  digestive  system  consists 
of  a  food  tube  known  as  the  alimentary  canal  and  certain 
masses  of  cells  known  as  digestive  glands. 

When  the  fish  swallows  food,  this  passes  from  the  mouth 
cavity  into  a  short  tube,  called  the  gullet,  and  thence  into  a 


\\vtv 

FIG.  98.  —  Internal  organs  of  a  fish.     (Carp.) 

comparatively  long  wide  stomach  (Fig.  98),  which  in  the 
carp  extends  half  the  length  of  the  body  cavity.  From  the 
stomach  extends  the  small  intestine,  which  turns  upon  itself 


FISHES  131 

several  times,  thus  forming  a  coil,  the  posterior  end  of  which 
finally  opens  to  the  exterior  just  in  front  of  the  anal  fin. 

In  the  inner  lining  of  the  stomach  and  intestine  are  special 
cells  which  make  up  digestive  glands.  These  have  the  power 
to  manufacture  digestive  ferments  (P.  B.,  53),  which  are 
forced  out  into  the  alimentary  canal  when  food  is  present. 
As  in  plants,  these  ferments  dissolve  the  foods  and  make  them 
ready  for  use  in  the  body.  In  addition  to  the  digestive 
glands  in  the  lining  of  the  alimentary  canal  there  are  glands 
outside  the  digestive  tube.  One  of  these  is  the  liver  (Fig.  98), 
which  secretes  bile.  This  is  carried  to  the  intestines  by  a 
tube  called  the  bile  duct.  In  the  liver  is  a  sac  (bile  sac) 
(Fig.  98)  which  holds  any  excess  of  bile.  When  the  food  has 
been  digested  it  is  absorbed  by  thin-walled  blood  vessels 
found  in  the  lining  of  the  alimentary  canal,  and  so  passes 
into  the  blood  to  be  distributed  around  the  body. 

99.  Blood  and  circulation.  —  Instead  of  ducts  and  sieve 
tubes  (P.  B.,  Figs.  14,  15,  16)  as  in  the  seed  plants  we  studied, 
the  fish  has  blood  vessels  to  distribute  digested  foods  to  various 
parts  of  the  body.  In  addition  to  these  the  fish  possesses  a 
heart  (Fig.  99),  which  aids  in  pumping  or  forcing  the  blood 
through  blood  vessels,  thus  keeping  it  in  constant  motion. 
The  blood  vessels  are  of  three  kinds ;  namely,  arteries,  capil- 
laries, and  veins.  The  arteries  have  muscular  and  elastic 
walls  which  contract  and  so  aid  the  heart  in  forcing  the  blood 
along  its  course.  The  arteries  always  carry  the  blood  away 
from  the  heart,  and  they  subdivide  into  smaller  and  smaller 
tubes.  At  the  ends  of  the  smallest  arteries  are  tiny,  short, 
thin-walled  blood  vessels,  known  as  capillaries.  Capillaries 
permit  the  digested  food  to  osmose  through  their  walls  into 
the  adjacent  cells,  and,  in  turn,  absorb  waste  matters  from 
the  cells. 


132 


ANIMAL  BIOLOGY 


FIG.  99.  —  Diagram  of  the  circula- 
tion of  a  fish. 


The  blood  passes  from  the 
capillaries  into  the  veins,1 
which  are  thinner-walled  than 
the  arteries.  These  veins  carry 
the  blood  back  to  the  heart. 
The  heart  (Fig.  100)  consists  of 
two  principal  parts;  a  thin- 
walled  auricle  which  receives 
blood  from  the  veins,  and  a 
thick-walled,  muscular  portion 
called  the  ventricle,  which 
forces  the  blood  out  into  the 
arteries. 

100.  Adaptations  for  breath- 
ing. —  Laboratory  study. 

1.  Raise  the  gill  covers  of  a 

preserved  fish  and  find 
the  gills.  Carefully 
separate  the  gills  with 
the  forceps.  How 
many  gills  are  present 
on  each  side? 

2.  The  openings  between  the 

gills  are  called  gill 
clefts.  Gently  push  a 
thin  strip  of  wood  or 
the  forceps  through 
one  of  the  gill  clefts 
as  far  as  you  can. 
a.  In  what  cavity  do  the 
forceps  or  strip  of 
wood  appear  ? 

1  This  is  true  of  all  organs  of 
the  fish,  excepting  the  gills.  See 
101. 


FISHES  133 

6.   Describe  the  situation  of  the  gills  with  reference  to 
the  mouth  cavity. 

3.  Hold  the  preserved  fish  with  its  mouth  upward  and  care- 

fully pour  water  into  the  mouth  opening.  Where 
does  the  water  come  out  ? 

4.  Place  a  gill  that  has  been  removed  from  a  fish  (a  salmon 

if  possible)  in  a  watch  glass  and  cover  it  with  water. 
Find  the  following  parts  :  (l)a  soft  part  made  up  of 
slender  divisions  called  gill  filaments.  (2)  a  curved 
part  to  which  the  gill  filaments  are  attached,  known  as 
the  gill  arch,  and  (3)  projections  on  the  side  opposite 
the  gill  filaments  which  are  known  as  gill  teeth  or  rakers. 

a.  Is  the  gill  arch  relatively  hard  or  soft  compared  to  the 

filaments  ? 

b.  Are  the  gill  teeth  or  rakers  relatively  hard  or  soft? 

c.  Look  again  at  the  perch  and  state  whether  the  rakers 

are  found  on  the  side  of  the  arch  nearest  to  the 
mouth  cavity  or  on  the  opposite  side. 
What  is  the  use  of  the  gill  teeth  when  the  fish  takes 
in  a  mouthful  of  water  containing  food,  and  does 
not  wish  to  swallow  the  water? 

d.  Make  a  sketch  (about  four  inches  long)  of  a  gill  to 

show  the  shape  of  the  whole  and  the  structure  of  a 
small  portion.  Label  gill  arch,  gill  filaments,  gill 
rakers. 

5.  The    gill    filaments    contain    thin-walled    blood    vessels 

(capillaries)  which  are  separated  from  the  water  by 
a  thin  membrane.  The  heart  forces  the  blood 
into  certain  arteries  that  carry  it  to  the  capil- 
laries in  the  gills  and  thence  blood  passes  back  to 
the  body  through  another  set  of  arteries.  (Fig.  100.) 
Bearing  in  mind  that  breathing  is  essentially  the 
same  in  animals  as  in  plants  (P.  B.,  82),  — 

a.  What  gas  will  the  blood  bring  from  the  body  to  be 

given  off  in  the  gills  in  the  process  of  breathing  ? 

b.  What  gas  is  taken  up  by  the  blood  in  the  gills  to  be 

carried  around  through  the  body? 

c.  How  are  the  gill  filaments  (as  stated  above)  fitted  by 

structure  to  permit  this  interchange  of  gases  ? 


134 


ANIMAL  BIOLOGY 


6. 


d.  How  are  the  delicate  gill  filaments  protected  from 
injury? 

If  the  same  water  remained  on  the  gills  for  some  time,  what 
changes  in  the  relative  amount  of  oxygen  and  car- 
bon dioxid  in  the  water  would  occur  ?  Why,  then, 
is  it  necessary  that  a  current  of  water  should  pass 
over  the  gills  ? 


\r\yc\s 


FIG.  100.  —  Diagram  of  the  circulation  of  blood  in  the  gill  of  a  fish. 

7.  Describe  the  movements  of  the  jaws  and  gill  covers  of  a 

living  goldfish  when  it  is  breathing.  (If  the  fish 
has  been  in  a  jar  of  water  without  green  plants  for 
some  time,  these  movements  will  be  more  pro- 
nounced.) 

8.  Watch  the  fish  as  it  opens  its  mouth. 

a.  Is  the  size  of  the  mouth  cavity  now  greater  or  less  than 

it  was  when  closed  ? 

b.  Why  does  the  water  now  enter  the  mouth?     (The 

inward  movement  of  the  water  may  be  demonstrated 


FISHES  135 

more  easily  if  some  powdered  carmine  is  stirred  into 

the  water.) 
c     What  will  the  incoming  current  of  water  bring  to  the 

gill  filaments  ? 
9.   Watch  the  fish  as  it  closes  its  mouth. 

a.   Is  the  size  of  the  mouth  cavity  now  greater  or  less 

than  it  was  before  ? 
6.    Why  do  the  gill  covers  now  open  ? 
c.    What  will  the  current  of  water  carry  away  from  the 

gill  filaments  ? 

101.  Respiration  and  the  production  of  energy.  —  We 
have  just  seen  that  when  the  goldfish  takes  hi  a  mouth- 
ful of  water  and  then  closes  its  mouth,  the  water  is  forced 
over  the  gills,  thus  bringing  oxygen  to  the  filaments.  The 
capillaries  in  the  filaments  absorb  the  oxygen,  and  the  blood 
then  passes  on  into,  other  arteries  which  carry  it  all  over  the 
body  of  the  fish.  In  the  capillaries  at  the  ends  of  the  small- 
est arteries  the  oxygen  passes  into  the  cells  as  does  the  food. 
Now  what  becomes  of  the  oxygen  ? 

As  in  plants  (P.  B.,  80),  the  oxygen  unites  with  ele- 
ments in  the  foods  and  in  the  protoplasm  of  the  cells  and 
produces  oxidation  and  liberation  of  energy,  which  gives 
the  fish  the  power  to  contract  its  muscles  and  so  to  push 
against  the  water  with  its  tail  and  tail  fin,  thus  propelling  the 
animal  in  any  direction,  or  to  open  its  jaws  and  shut  them  on 
another  fish,  thus  securing  food.  In  fact,  all  the  work  that 
the  fish  performs  is  made  possible  through  the  burning  of 
its  foods  or  protoplasm  by  the  oxygen. 

Since  the  proteins,  fats,  carbohydrates,  and  protoplasm 
all  contain  carbon,  when  these  are  oxidized,  carbon  dioxid 
(CO2)  is  formed  as  one  of  the  waste  substances.  All  the 
waste  substances  pass  out  of  the  cells,  through  the  walls  of 
the  capillaries,  into  the  blood,  which  passes  on  into  the  veins 
and  back  to  the  heart.  The  heart  contracts  and  drives  the 


136  ANIMAL  BIOLOGY 

blood  loaded  with  carbon  dioxid  out  into  the  arteries,  which 
carry  it  to  the  capillaries  of  the  gills  (Fig.  100).  Here  the 
waste  matters  pass  out  into  the  water,  which  is  then  forced 
out  by  the  closing  of  the  mouth  past  the  gill  coverSo 

102.  Adaptations  for  sensation.     (Optional.) 

1.  Study  the  eye  of  a  goldfish. 

a.  Describe  its  position,  shape,  and  size  relative  to  that  of  the 

head. 

b.  Notice  that  the  eye  consists  of  a  black  center  (the  pupil) 

through  which  light  enters  the  eye,  and  a  colored  iris. 
Add  these  features  to  the  drawing  of  the  goldfish 
(91,  5),  and  label  each. 

2.  The  nostrils  lie  in  front  of  the  eyes,  and  as  they  are  small,  a 

preserved  fish  head  may  help  in  locating  them.  (In 
the  perch  there  are  two  on  each  side.) 

a.  Show  in  your  drawing  the  position,  shape,  and  size  of  the 

nostril  of  one  side  and  label. 

b.  Gently  probe  the  nostril  of  a  preserved  fish  with  a  stiff 

bristle. 

(1)  Do  the  nostrils  open  into  the  mouth  or  not  ? 

(2)  Could  the  nostrils  be  used  in  breathing  ?    Give  reason 

for  your  answer. 

(3)  Bearing  in  mind  the  common  uses  of  nostrils  of  higher 

animals,  state  which  of  these  is  the  probable  function 
of  the  nostrils  of  a  fish. 

103.  Senses  of  fishes.  — -  Fishes  are  said  to  possess  keen  sight. 
The  eyes,  however,  except  in  rare  cases,  are  only  fitted  for  seeing 
while  in  the  water.     These  organs  have  no  eyelids,  so  the  fish  always 
seems  Jo  be  wide  awake.     The  sense  of  smell  is  located  in  the  nos- 
trils, and  since  these  do  not  open  into  the  mouth  cavity,  this  is  the 
only  function  of  the  nostrils.     The  taste  sense  is  said  to  be  located 
in  the  outer  skin.     The  fish  has  no  external  ears ;   it  has,  however, 
internal  ears,  but  these  are  supposed  to  serve  as  balancing  organs, 


FISHES  137 

rather  than  as  organs  of  hearing.     Fishes  from  which  these  internal 
ears  have  been  removed  are  unable  to  maintain  their  equilibrium. 

Some  fishes  have  special  organs  that  serve  as  tactile  organs  such 
as  are  found  on  the  under  side  of  the  head  of  a  cod  (Fig.  108)  and  also 
on  the  headof  bullheads  (Fig.  101).  Along  each  side  of  the  body  and 
tail  of  fishes  is  a  series  of  little  openings  or  pores  which  form  what  is 
known  as  the  lateral  line  (Fig.  108).  These  organs  are  supposed  to  be 
principally  organs  of  touch. 


FIG.  101.  —  Bullhead.     (Goode.) 

104.  Reproduction  and  life  history.  —  The  flowers  of  seed 
plants  are  devoted  to  the  production  of  seeds  which,  in 
turn,  produce  new  plants  of  the  same  kind  (P.  B.,  83). 
Likewise  in  fishes  there  are  special  organs  the  sole  function 
of  which  is  the  production  of  new  individuals.  The  organs 
of  fishes  which  may  be  said  to  correspond  in  function  to  the 
stamens  and  pistils  of  flowers  are  the  ovaries  (Fig.  98)  and 
spermaries.  In  the  ovaries  are  produced  many  egg-cells, 
and  the  mass  of  eggs  in  the  ovary  of  a  fish  is  often  called  the 
roe.  In  order  that  an  egg  may  develop  it  must  first  be  fer- 
tilized by  a  sperm-cell  from  the  spermary  of  a  male  fish.  This 
process  usually  occurs  in  the  water  after  the  ripe  eggs  and 
sperm-cells  have  been  extruded  from  the  ovaries  and  sper- 
maries of  the  parent  fishes. 

You  will  recall  the  fact  that  the  pollen  tube  containing  a 
sperm-nucleus  makes  its  way  into  an  ovule  and  that  the 


138 


ANIMAL  BIOLOGY 


nucleus 

A,  sperm-cell  entering  an  egg-cell 


C,  sperm-nucleus  and 
egg-nucleus  uniting 


nucleus  of 

sperm-cell 


egg-nucleus 

B,    sperm-nucleus    approaching 
the  egg-nucleus 


--fertilized 
egg-nucleus 


D,  fertilized  egg-nucleus 
FIG.  102.  —  Fertilization  of  an  egg. 


developing 
embryo 


A,  four-celled  stage  of 
.embryo 


embryo 


C,    embryo    more    fully    de- 
veloped 


developing 
embryo 


B,  many-celled  stage  of 
embryo 


yolk,  food  \^v 

supply 

yolk  sac 

D,  young  fish  with  yolk  still  attached 
FIG.  103.  —  Development  of  a  fish  egg. 


FISHES 


139 


sperm-nucleus  is  forced  into  the  ovule  and  unites  with  the 
egg-nucleus ;  this  is  the  process  known  as  fertilization 
(P.  B.,  91).  In  the  case  of  fishes  the  sperm-cells  swim  to  the 
eggs,  and  then  force  their  way  into  the  egg  (Fig.  102,  A). 


FIG.  104.  —  Nest  of  stickleback.    Above,  male  entering  nest  with  eggs  ; 
below,  male  depositing  sperm-cells. 

The  nucleus  of  the  sperm-  and  egg-cells  then  unite  just  as  in 
plants  (Fig.  102,  B,  C,  D).  The  egg  nucleus  thus  fertilized 
first  divides,  and  then  the  cell  body,  and  thus  are  formed 
two  cells.  Each  of  these  cells  in  turn  divides,  and  so 
four  cells  are  produced  (Fig.  103,  A,  B).  The  process 'of 


140 


ANIMAL  BIOLOGY 


division  continues  until  a  many-celled  organism  is  de- 
veloped. 

•As  the  cells  increase  in  number,  they  become  different  in 
character  and  form  the  various  organs  of  the  body.  When 
the  little  fish  first  hatches,  and  begins  to  swim  about,  it 
often  has  attached  to  it  some  of  the  food  substance  (yolk) 
stored  in  the  egg  (Fig.  103,  D).  After  this  is  used  up,  the 
young  fish  must  secure  its  own  food. 

Most  fishes  do  not  take  any  care  of  their  eggs  or  young,  and 
in  some  cases  the  parents  die  soon  after  the  eggs  are  laid  and  \ 
fertilized.  In  the  case  of  the  stickleback,  however,  the  male 
fish  makes  a  nest  (Fig.  104)  in  which  the  females  deposit  their 
eggs.  The  male  then  extrudes  sperm  over  the  eggs.  The 
male  stays  about  the  nest  and  guards  the  eggs  and  also 

the  young  sticklebacks 
when  they  hatch  out. 

105.  Artificial  prop- 
agation of  fishes.  - 
Since,  as  we  have  said, 
most  kinds  of  fishes 
give  no  attention  to 
eggs  or  young,  enor- 
mous numbers  of  both 
eggs  and  young  are 
eaten  by  other  fishes ; 
hence,  only  a  small  pro- 
portion come  to  ma- 
turity. For  example, 

while  a  codfish  lays  8,000,000  eggs,  only  about  two  of 
these  eggs  on  the  average  come  to  maturity.  Hence,  in 
order  to  increase  to  any  considerable  extent  the  number  of 
fishes,  the  eggs  are  artificially  hatched.  That  is,  the  fish 


FIG.    105.  —  Artificial    fertilization    of    eggs. 
(Coleman.) 


FISHES  141 

are  caught  when  the  eggs  are  ripe  and  the  eggs  are  gently 
squeezed  from  the  ovaries  into  the  water  (Fig.  105).  Then 
some  of  the  sperm-cells  are  similarly  squeezed  from  the  male 
fish  and  mixed  with  the  eggs.  This  provides  for  fertilizing 
most  of  the  eggs,  which  would  probably  not  occur  in  nature. 
Special  apparatus  is  devised  for  keeping  the  eggs  supplied 
with  fresh  water  until  they  hatch  (Fig.  106).  When  the 


FIG.  106.  —  Interior  of  fish  hatchery. 

young  are  old  enough  they  are  fed  for  a  time,  then  the  young 
fry,  are  set  free  in  the  waters  where  more  fish  are  desired. 
Millions  of  young  fish  are  every  year  distributed  by  the 
government  all  over  the  United  States  to  be  placed  in  ponds, 
rivers,  and  lakes  where  the  supply  is  deficient,  or  in  the  ocean 
along  the  shore. 

106.  Economic  importance  of  fishes.  —  From  very,  ancient 
times  fishes  have  formed  a  considerable  part  of  the  food  of 
peoples  that  lived  near  bodies  of  water.  The  importance  to 


142  ANIMAL  BIOLOGY 

man  of  fishes  as  a  source  of  food  can  scarcely  be  overesti- 
mated. Unlike  domestic  animals,  the  fishes  grow  to  maturity 
without  any  care  on  the  part  of  man.  The  fisherman  has 
only  to  provide  the  means  to  gather  his  harvest,  while  the 
herdsman  must  care  for  his  flocks  and  herds  the  year  round. 
Thus  we  see  why  fish  are  cheaper  than  other  forms  of  flesh 
food. 

While  fish  are  most  important  to  man  as  food,  they  have 
other  uses.  Thus,  for  instance,  the  menhaden  are  caught 
scarcely  at  all  for  food,  but  for  the  large  quantities  of  oil 
extracted  from  them.  The  remainder  of  their  bodies  is  used 
as  fertilizer.  It  is  estimated  that  about  3,000,000  gallons  of 
oil  and  1,000,000  tons  of  scrap,  with  a  total  value  of  $2,500,000 
is  obtained  annually  by  American  fishermen  from  this  kind 
of  fish.  The  oil  extracted  from  the  livers  of  cod  forms  a 
valuable  food  preparation  for  invalids,  since  it  is  said  to  be 
more  easily  absorbed  and  oxidized  than  any  other  known 
fat. 

The  great  importance  of  fishes,  however,  is  due  to  the  fact 
that  they  furnish  a  cheap  and  wholesome  food.  Nearly  all 
the  parts  of  a  fish  are  thus  used.  Not  only  is  the  flesh  eaten, 
but  also  the  eggs  (roe).  The  swim  bladders,  too,  of  many 
fishes  are  made  into  isinglass  which  yields  the  highest  grade 
of  gelatin.1  Fish  are  eaten  not  only  in  a  fresh  condition,  but 
are  also  prepared  in  various  ways.  Among  these  methods 
of  preservation  are  drying,  smoking,  pickling,  and  canning. 
Two  of  the  more  important  fisheries  are  those  of  the  salmon 
and  the  cod. 

107.  The  salmon.  —  The  salmon  (Fig.  107)  is  doubtless 
the  most  important  food  fish  of  the  world,  and  the  Pacific 
salmon  completely  outclasses  all  other  forms.  The  Atlantic 

1  See  article  on  isinglass  in  Cyclopedia. 


FISHES  143 

salmon  was  once  very  abundant,  but  is  gradually  diminishing 
in  numbers  for  reasons  that  will  be  mentioned  later  (110). 
"  The  salmon  were  made  for  the  millions.  The  Siwash 
Indian  eats  them  fresh  in  summer,  dries  them,  or  later  on 
freezes  them,  for  himself  and  his  dogs  in  winter.  The  epicure 
pays  for  having  the  fresh  fish  shipped  in  ice  to  his  table, 
wherever  that  table  may  happen  to  be.  In  mid-ocean,  the 
great  American  canned  salmon  is  often  the  best  and  only 
fish  afloat.  In  the  jungles  of  the  Far  East,  in  the  frontier 


FIG.  107.  —  The  Salmon.    (Jordan  and  Evermann.    Courtesy  of  Doubleday, 

Page  &  Co.) 

bazaar  of  the  enterprising  Chinese  trader,  it '  bobs  up  serenely ' 
to  greet  and  cheer  the  lonesome  white  man  who  is  far  from 
home  and  meat  markets.  Even  in  the  wilds  of  Borneo  its 
name  is  known  and  respected;  and  he  who  goes  beyond 
the  last  empty  salmon  tin,  truly  goes  beyond  the  pale  of 
civilization.  The  diffusion  of  knowledge  among  men  is 
not  much  greater  than  the  diffusion  of  canned  salmon;  and 
the  farther  Americans  travel  from  home,  the  more  they  re- 
joice that  it  follows  the  flag. 

"  The  common  salmon  of  Europe,  and  also  of  Labrador 
and  New  England,  was  accounted  a  wonderful  fish  both  for 
sport  -and  for  the  table,  until  the  discovery  of  the  salmon 


144  ANIMAL  BIOLOGY 

millions  of  the  Pacific  Coast  cheapened  the  name.  To  hold 
their  place  in  the  hearts  of  sportsmen,  game  fishes  must  not 
inhabit  streams  so  thickly  that  they  are  crowded  for  room, 
and  can  be  caught  with  pitchforks.  Yet  this  once  was  true 
of  the  salmon  in  several  streams  of  the  Pacific  Coast.  The 
bears  of  Alaska  grow  big  and  fat  on  the  salmon  which  they 
catch  with  the  hooks  that  Nature  gave  them."  l 

The  Pacific  salmon  are  caught  in  the  rivers  that  empty 
into  the  Pacific  Ocean,  such  as  the  Columbia,  Sacramento, 
and  Yukon.  The  salmon  reach  their  maturity  in  the  ocean. 
When,  however,  the  spawning  time  approaches,  the  salmon 
make  their  way  in  great  numbers  to  the  mouths  of  rivers 
like  the  Columbia  and  proceed  up  these  streams,  leaping 
seemingly  impassable  waterfalls  in  order  to  reach  the  head- 
waters. Here  the  sand  is  scooped  out  by  the  male,  and 
the  female  salmon  deposits  her  eggs  and  the  male  the 
fertilizing  sperm-cells.  The  fertilized  eggs  are  then  covered 
with  sand.  The  parent  fish  soon  die ;  none  ever  reach  the 
ocean  again.  After  the  eggs  hatch,  the  young  slowly  float 
down  the  stream  to  the  ocean  to  repeat  the  life  of  their 
parents. 

It  is  when  the  fish  are  proceeding  up  the  rivers  that  they 
are  caught.  Sometimes  they  are  so  abundant  that  the  river 
seems  to  be  choked  with  them.  Salmon  are  shipped  fresh  in 
ice.  Enormous  quantities  are  'also  canned  and  smoked.  The 
estimated  value  of  the  annual  catch  of  Pacific  salmon  varies 
from  $10,000,000  to  $15,000,000. 

108.  The  codfish.  —  Next  in  importance  to  the  salmon, 
at  least  in  the  United  States,  is  the  cod  (Fig.  108),  for  which 
the  fishermen  receive  about  $3,000,000.  Other  countries 
engaged  in  the  cod  fisheries  are  Newfoundland,  Canada,  Nor- 

1  From  Hornaday's  "American  Natural  History." 


FISHES  ,  145 

way,  Sweden,  Great  Britain,  and  France.  The  catch  of 
cod  for  the  world  is  estimated  to  be  $20,000,000  annually. 
Codfish  are  found  in  the  northern  part  of  both  the  Atlantic 
and  Pacific  Oceans,  but  the  Alaskan  cod  is  not  considered  to 
be  as  fine  a  food  fish  as  the  Atlantic  species. 


FIG.  108.  — The  codfish.     (Goode.) 

The  cod  is  a  deep  water  fish  and  is  usually  caught  in  from 
thirty  to  seventy  fathoms  (a  fathom  being  six  feet).  Cod 
are  caught  off  the  coast  of  Newfoundland,  and  during  the 
winter  as  far  south  as  the  Middle  States.  "  From  the  earliest 
settlement  of  America  the  cod  has  been  the  most  valuable  of 
our  Atlantic  Coast  fishes.  Indeed  the  codfish  of  the  Banks 
of  Newfoundland  was  one  of  the  principal  inducements  which 
led  England  to  establish  colonies  in  America,  and  in  the  rec- 
ords of  early  voyages  are  many  references  to  the  abundance 
of  codfish  along  our  shores.  ...  So  important  was  the  cod 
in  the  early  history  of  this  country  that  it  was  placed  upon 
the  colonial  seal  of  Massachusetts,  and  it  was  also  placed 
upon  a  Nova  Scotian  bank  note,  with  the  legend  '  Success  to 
the  Fisheries.'  "l 

The  average  weight  of  large  cod  is  said  to  be  from  twenty 

1  From  Jordan  and  Evermann's  "American  Food  and  Game 
Fishes."  Every  student  of  this  fish  work  should  read  Kipling's 
"Captains  Courageous"  for  description  of  the  cod  fisheries  on  the 
Grand  Banks. 


146 


ANIMAL   BIOLOGY 


to  thirty-five  pounds,  depending  on  the  locality.  The  aver- 
age weight  of  small  cod  is  twelve  pounds.  Jordan  and  Ever- 
mann  state  that  cod  weighing  75  pounds  are  not  common, 


FIG.  109.  —  The  shad.     (Goode.) 


but  that  one  was  caught  off  the  New  England  coast  that 
weighed  21 1J  pounds. 

Codfish  are  marketed  fresh,  pickled,   salted,  and   dried. 
Oil  and  isinglass  are  also  obtained  from  the  cod. 


FIG.  110.— The  herring. 


(Jordan  and  Evermann. 
Page  &  Co.) 


Courtesy  of  Doubleday, 


109.  Library  study  of  other  fishes.  —  (Optional.) 
Consult  Jordan  and  Evermann's  "  American  Food  and  Game 
Fishes,"  Hornaday's  "  American  Natural  History,"  and  special 
articles  in  Cyclopedias  or  other  reference  books,  on  one  or  more  of 
the  following  fishes :  mackerel  (Fig.  95),  sardine,  shad  (Fig.  109), 
herring  (Fig.  110),  white  fish,  smelt,  bluefish,  halibut,  menhaden. 
Write  in  your  notebook  an  account  of  the  fishes  selected  for  study, 
using  the  following  topics  as  a  guide :  — 


FISHES  147 

1.  General  appearance  (size,  color,  general  form). 

2.  Geographical  distribution  (that  is,  hi  what  waters  the  fishes 

are  found). 

3.  Food  and  feeding  habits. 

4.  Method  of  capturing  the  fish. 

5.  Amount  caught  annually  and  its  value  hi  money. 

6.  Breeding  habits  and  other  general  facts  of  interest. 

If  possible  illustrate  your  composition  with  any  drawings  or  pic- 
tures of  the  fish  you  are  studying. 

110.  Visit  to  a  fish  market.  —  (Optional.) 

In  your  notebook  prepare  an  account  of  your  visit  to  some  fish- 
market,  using  the  following  topics  as  a  guide. 

1.  Location  of  the  fish  market  and  the  name  of  its  owner. 

2.  Make  a  list  of  the  various  kinds  of  fish  offered  for  sale. 

3.  State  the  kind  of  fish  that  sells  at  the  lowest  price  per  pound  at 

this  time  of  year. 

4.  State  the  kind  of  fish  that  is  most  expensive  per  pound  at  this 

season. 

5.  Name  the  kind  of  fish  now  sold  in  the  greatest  quantity. 

111.  Conservation  of  food  fishes.  —  A  story  of  reckless 
waste  similar  to  that  recorded  in  regard  to  the  destruction 
of   our   forests   may   be   duplicated    here    concerning    the 
way  men  have  exploited   our  abundant   natural  source  of 
food,   the   fishes.     The   Atlantic   salmon,  which   was  once 
"  the  salmon,"  is  now  of  comparatively  little  commercial 
importance.     "  Salmon  were  marvelously  abundant  in  colo- 
nial days.  ...     It  is  stated  that  the  epicurean  apprentices 
of  Connecticut  would  eat  salmon  no  oftener  than  twice  a 
week.  .  .  .     There  can  be  no  doubt  that  one  hundred  years 
ago  salmon  fishing  was  an  important  food  resource  in  south- 
ern New  England.  .  .  .     But  at  the  beginning  of  this  century 
salmon  began  rapidly  to  diminish.     Mitchill  stated  in  1814 
that  in  former  days  the  supply  to  the  New  York  market 


148  ANIMAL  BIOLOGY 

usually  came  from  the  Connecticut,  but  of  late  years  from 
the  Kennebec,  covered  with  ice.  Rev.  David  Dudley  Field, 
writing  in  1819,  states  that  salmon  had  scarcely  been  seen 
in  the  Connecticut  for  fifteen  or  twenty  years.  The  cir- 
cumstances of  their  extermination  in  the  Connecticut  are 
well  known,  and  the  same  story,  with  names  and  dates 
changed,  serves  equally  well  for  other  rivers. 

"  In  1798  a  corporation,  known  as  the  '  Upper  Locks  and 
Canal  Company,'  built  a  dam  sixteen  feet  high  at  Millers 
River,  100  miles  from  the  mouth  of  the  Connecticut.  For 
two  or  three  years  fish  were  seen  in  great  abundance  below 
the  dam,  and  for  perhaps  ten  years  they  continued  to  appear, 
vainly  striving  to  reach  their  spawning  grounds;  but  soon 
the  work  of  the  extermination  was  complete.  When,  in 
1872,  a  solitary  salmon  made  its  appearance,  the  Saybrook 
fishermen  did  not  know  what  it  was."  1 

The  Pacific  salmon  is  rapidly  disappearing  also.  "  Natu- 
rally the  salmon  millions  of  the  Pacific  streams  early  attracted 
the  attention  and  aroused  the  avarice  of  men  who  exploit 
the  products  of  nature  for  gain.  As  usual,  the  bountiful 
supply  begat  prodigality  and  wastefulness.  The  streams 
nearest  to  San  Francisco  were  the  first  to  be  depleted  by 
reckless  overfishing.  .  .  .  Regarding  the  conditions  that 
in  1901  prevailed  in  Alaska,  the  following  notes  .  .  .  are  of 
interest :  '  The  salmon  of  Alaska,  numerous  as  they  have 
been  and  in  some  places  still  are,  are  being  destroyed  at  so 
wholesale  a  rate  that  before  long  the  canning  industry  must 
cease  to  be  profitable,  and  the  capital  put  into  the  canneries 
must  cease  to  yield  any  return.' 

"  The  destruction  of  the  salmon  comes  about  through  the 
competition  between  the  various  canneries.  Their  greed  is 
so  great  that  each  strives  to  catch  all  the  fish  there  are,  and 

1  Jordan  and  Evermann's  "American  Food  and  Game  Fishes." 


FISHES  149 

all  at  one  time,  in  order  that  its  rivals  may  secure  as  few  as 
possible.  .  .  .  Not' only  are  salmon  taken  by  the  steamer 
load,  but  in  addition  millions  of  other  food  fish  are  captured, 
killed,  and  thrown  away.  At  times,  also,  it  happens  that  far 
greater  numbers  of  salmon  are  caught  than  can  be  used  be- 
fore they  spoil.  ...  In  many  of  the  small  Alaskan  streams 
the  canning  companies  built  dams  or  barricades  to  prevent 
the  fish  from  ascending  to  their  spawning  beds,  and  to  catch 
all  of  them.  In  some  of  the  small  lakes,  the  fishermen  actu- 
ally haul  their  seines  on  the  spawning  grounds. 

"  The  laws  passed  by  Congress  to  prevent  the  destruction 
of  the  Alaskan  salmon  fisheries  are  '  ineffective,  and  there  is 
scarcely  a  pretense  of  enforcing  them/  To-day  the  question 
is  —  will  lawless  Americans  completely  destroy  an  industry 
which  if  properly  regulated,  will  yield  annually  $13,000,000 
of  good  food  ?  Will  the  salmon  millions  of  the  Pacific  share 
the  fate  of  the  buffalo  millions  of  the  Great  Plains?  At 
present  it  seems  absolutely  certain  to  come  to  pass.  .  .  .  The 
time  for  strong,  effective,  and  far-reaching  action  for  the 
protection  of  that  most  valuable  source  of  cheap  food  for 
the  millions  is  now!"  1 

Many  of  the  states  have  passed  laws  for  the  protection  and 
conservation  of  game  fishes  such  as  trout  and  bass.  The 
sportsmen  have  seen  to  this ;  and  while  it  is  desirable  that 
these  forms  of  wild  life  should  be  preserved  and  their  number 
increased  in  all  our  waters,  it  is  of  much  greater  importance 
that  the  fishes  which  supply  food  for  the  millions  should  not 
be  left  to  the  mercy  of  such  utterly  selfish  men  as  those 
responsible  for  the  rapid  depletion  of  the  Atlantic  salmon  and 
the  rapid  decrease  of  the  Pacific  salmon. 

It  is  necessary  not  only  that  the  number  of  all  fish  desirable 
for  food  should  be  increased  by  means  of  artificial  propaga- 
1  Hornaday's  "The  American  Natural  History." 


150  ANIMAL  BIOLOGY 

tion  as  indicated  in  105,  but  also  that  wise  laws  governing 
the  catching  of  fish  should  be  passed  and  rigidly  enforced. 
The  United  States  government  has  done  and  is  still  doing 
splendid  work  in  the  artificial  propagation  and  distribution 
of  fishes  through  the  agency  of  the  thirty-nine  fish-hatching 
stations  of  the  Bureau  of  Fisheries,  but  has  done  little  or 
nothing  in  the  regulation  of  the  fish  industry.  This  has  been 
left  to  the  initiative  of  the  states.  Following  are  some  of  the 
regulations  that  many  of  the  states  have  embodied  in  laws : 
(1)  There  must  be  no  obstruction  in  rivers  that  would  pre- 
vent fish  from  moving  freely  up  and  down  streams  either 
to  spawn  or  to  search  for  food.  If  dams  are  built,  runways 
must  also  be  constructed  permitting  the  free  passage  of 
fish.  (2)  Fish  must  not  be  caught  at  the  spawning  season, 
otherwise  the  future  supply  is  endangered.  (3)  No  methods 
of  fishing  should  be  employed  in  which  immature  fish  are 
caught  or  killed.  Such  methods  are  (a)  exploding  dynamite 
in  the  water,  thus  killing  all  kinds  and  sizes  of  fish  indis- 
criminately; (6)  catching  fishes  with  nets  the  meshes  of 
which  are  so  small  that  immature  fish  are  caught  as  well  as 
mature;  (c)  wholesale  and  mechanical  devices  of  catching 
fish  such  as  the  fishing  wheel,  for  by  this  device  the  fish  have 
no  chance  for  escape.  (4)  Fishermen  must  not  keep  fish 
even  when  caught  if  they  are  undersized.  (5)  It  should 
be  illegal  to  destroy  any  food  fish  or  use  it  for  any  purpose 
other  than  food. 

These  laws  are  enforced  by  state  fish  and  game  wardens 
provided  there  is  public  demand  for  their  enforcement. 
The  necessity  for  the  enforcement  of  these  regulations  will 
be  obvious,  not  only  in  waters  over  which  the  states  have 
jurisdiction,  but  also  in  the  waters  controlled  by  the  United 
States  government. 


CHAPTER  V 
CRAYFISHES  AND   THEIR  RELATIVES 

112.   A  study  of  the  crayfish.  —  Laboratory  study. 

A.  Regions.  —  The  body  of  the  crayfish  has   two  distinct 

regions.  The  dorsal  surface  and  sides  of  the 
anterior  region  are  covered  by  a  cape,  consist- 
ing of  a  single  piece  of  shell-like  material.  This 
region  is  the  cephalothorax  (from  Greek  = 
head-thorax) .  The  posterior *  region  is  the 
abdomen. 

1.  Which  region  is  composed  of  a  number  of  similar 

segments  ? 

2.  Which   region  has  the   legs,  antennae  (feelers),  and 

eyes  attached  to  it  ? 

B.  Adaptations  for  walking. 

Place  a  crayfish  in  the  center  of  a  pan  with 
enough  water  to  cover  the  animal.  If  the  cray- 
fish does  not  walk,  touch  it  with  the  pincers. 

1.  How  many  pairs  of  legs  are  used  in  walking? 

2.  In  what  directions  (forward,  backward,  or  sideways) 

are  you  able  to  get  the  crayfish  to  walk? 

3.  State  whether  or  not  the  "  large  claws  "  are  used  in 

walking. 

4.  Are  the  walking  legs  composed  of  one  piece  or  of 

several  movable  parts?  Of  what  advantage 
is  this  to  the  animal  ? 

5.  (Optional.)    Make  a  sketch  ( x2)  of  one  of  the  legs  to  show 

its  structure. 

1  The  meaning  of  each  of  these  terms  is  explained  in  6. 
151 


152  ANIMAL  BIOLOGY 

C.   Adaptations  for  swimming. 

Place  an  active  crayfish  in  a  pan  nearly 
filled  with  water.  Use  the  following  means 
to  get  it  to  swim :  make  a  sudden  movement 
toward  it  with  the  forceps  or  pencil;  if  this 
does  not  succeed,  take  hold  of  the  animal  near 
the  anterior  end  where  you  can  press  the  large 
pincers  against  the  body.  Do  this  quickly  and 
release  the  animal.  This  action  may  cause  the 
crayfish  to  swim  in  order  to  escape.  If  you 
cannot  get  this  crayfish  to  swim,  try  another. 

1.  In  what  direction  does  the  crayfish  swim? 

2.  State  whether  or  not  the  legs  are  used  in  swimming. 

3.  Watch  the  segments  of  the  abdomen  and  the  large 

appendages  at  the  posterior  end  to  determine 
their  action  in  swimming. 

a.  Describe  the  direction  of  the  movements  of  these 

parts. 

b.  Are  these  movements  made  slowly  or  quickly? 

4.  In  what  direction  will  the  doubling  under  of  the  ab- 

domen tend  to  send  the  animal  ? 

5.  In  what  direction  will  the  straightening  out  of  the 

abdomen  tend  to  send  the  animal  ? 

6.  In  what  direction,  therefore,  must  the  crayfish  strike 

the  harder  and  quicker  in  order  to  swim  back- 
wards ? 

7.  What  difference  is  there  in  the  shape  of  the  ventral 

surface  and  the  dorsal  surface  of  the  abdomen  ? 

8.  Which  surface  of  the  abdomen  will  enable  the  cray- 

fish to  get  the  better  hold  upon  the  water  ? 

9.  (Optional.)     Straighten  out  and  double  up  the  segments  of 

the  abdomen,  noting  how  the  segments  are  con- 
nected. Describe  now  all  the  adaptations  of  the 
abdomen  and  its  appendages  for  swimming  ? 
10.  (Optional.)  The  first  segment  of  the  abdomen  (next  to  the 
cephalothorax)  fits  under  the  cape ;  the  last  is  un- 
like the  others  in  shape,  being  quite  flat.  Straighten 


CRAYFISHES  AND    THEIR  RELATIVES  153 

out  and  double  up  the  parts  of  the  abdomen;   of 
how  many  segments  is  it  composed  ? 

11.  (Optional.)  The  large  appendages  (large  swimmerets)  and 
the  last  segment  of  the  abdomen  taken  together  are 
called  the  tail  fin.  Make  a  sketch  ( x  2)  of  the  abdo- 
men and  the  large  swimmerets.  Label:  first 
segment,  last  segment,  large  swimmerets,  tail  fin. 

D.   Adaptations  for  breathing. 

To  the  Teacher.  —  Prepare  some  preserved  cray- 
fishes in  the  following  manner :  Insert  the  point  of 
the  scissors  beneath  the  posterior  margin  of  the  cape 
that  covers  the  cephalothorax  and  halfway  between 
the  middle  line  of  the  dorsal  surface  and  the  lower 
margin  of  the  cape ;  cut  forward  to  the  front  end  of 
the  cape  and  remove  the  piece  of  shell. 

1.  Immerse  in  water   a  crayfish  prepared  as  directed 

above.  Examine  and  describe  the  structures  that 
you  find  above  the  legs  on  the  side  where  the 
cape  has  been  partially  removed.  These  struc- 
tures are  the  special  breathing  organs  of  the 
crayfisli.  They  are  known  as  gills. 

2.  Push  the  gills  to  one  side  and  find   the  soft  body 

wall.  Higher  up  find  the  line  of  attachment 
between  the  shell  and  the  body  wall.  You 
will  see  that  the  gills  are  not  inside  the  body, 
but  in  a  space  between  the  body  of  the 
animal  and  its  shell.  This  space  is  called  the 
gill  chamber. 

a.  In  what  region  of  the  crayfish  are  the  gill  chambers 
found? 

6.  What  forms  the  outer  wall  of  each  gill  chamber  ? 
What  forms  the  inner  wall  ? 

c.  Lift  up  the  cape  on  the  opposite  side  of  the  animal  ; 
state  where  it  is  free  from  the  body  wall. 

3.  Examine  the  gills  on  a  leg  that  has  been  removed 

from  the  thorax  and  floated  on  water  and  note 


154  ANIMAL  BIOLOGY 

that  it  is  largely  composed  of  numerous  slender 
divisions,  called  the  gill  filaments. 
Make  a  sketch  of  the  leg  ( X  2)  with  the  gills  at- 
tached and  label  gill  filaments. 

4.  The  gills  are  furnished  with  numerous  minute  thin- 

walled  blood  vessels  and  the  blood  in  them  is 
separated  from  the  water  only  by  a  thin  mem- 
brane. The  blood  flows  into  the  gills  from  all 
parts  of  the  body  by  one  set  of  blood  vessels 
and  leaves  the  gills  by  another.  Bearing  in 
mind  that  breathing  is  essentially  the  same  in 
animals  as  in  plants  (P.  B.,  82), — • 

a.  What  gas  will  the  blood  bring  from  the  body  to 

be  given  off  in  the  gills  in  the  process  of  breath- 
ing? 

b.  What  gas  is  taken  up  by  the  blood  in  the  gills  to 

be  carried  around  the  body? 

c.  How  are  the  gill  filaments  (as  stated  above)  fitted 

by  structure  to  permit  this  interchange  of 
gases  ? 

d.  How  are  the  delicate  gill  filaments  protected  from 

injury? 

5.  If  the  same  water  remained  on  the  gills  for  some  time, 

what  changes  in  the  relative,  amounts  of  oxygen 
and  carbon  dioxid  in  the  water  would  occur? 
Why,  then,  is  it  necessary  that  a  current  of 
water  should  pass  over  the  gills? 

6.  Do  currents  of  water  pass  through  the  gill  chamber  f 

-  Demonstration. 

Inject  some  harmless  coloring  matter,  such  as 
powdered  carmine  in  water,  into  the  posterior 
end  of  the  gill  chamber.  Place  the  crayfish 
again  in  water. 

a.  State  what  was  done  in  this  experiment. 

b.  Give  your  observations  and  conclusion. 

c.  What  will  the  incoming  current   of  water  bring 

to  the  gill  filaments  ? 

d.  What  will  the  current  of  water  carry  away  from 

the  gill  filaments  ? 


CRAYFISHES  AND   THEIR   RELATIVES  155 

7.  How  the  crayfish  causes  a  current  of  water  to  pass 

through  the  gill  chambers. 

To  the  Teacher.  —  Prepare  several  living  crayfish  so 
that  the  action  of  the  gill  bailer  may  be  seen.  To  do 
this  carefully  cut  off  a  small  part  of  the  anterior  por- 
tion of  the  shell  just  over  the  gill  scoop. 

Watch  the  movements  of  the  small  blade-like  body 
in  the  front  of  the  gill  chamber.  This  body  is 
the  gill  bailer,  or  gill  scoop. 

a.  Describe  the  movements  of  the  gill  scoop,  or  gill 

bailer. 

b.  When  it  moves  upward  and  forward,  what  effect 

will  the  gill  bailer  have  on  the  water  in  front 
of  it  and  in  the  gill  chamber  ? 

c.   Where  can  water  enter  the  gill  chamber  ?     (See 
D,  2,  c.) 

8.  (Optional.)     The  gill  bailer  is  a  part  of  one  of  the  crayfish's 

mouth  parts,  known  as  the  second  maxilla.  Exam- 
ine a  second  maxilla  that  has  been  removed  from 
the  head  thorax  of  a  preserved  crayfish.  Place  it 
in  a  watch  glass  half  filled  with  water  and  make  out 
the  following  parts  :  — 

a.  A  part  shaped  something  like  a  bird's  wing,  composed  of 

several  pieces. 

b.  The  gill  bailer  that  you  have  already  seen. 

c.  The  part  where  the  second  maxilla  was  torn  from  the 

body,  clearly  shown  by  the  shreds  of  muscle. 
When  you*  have  made  out  these  parts,  make  a  sketch 
of  the  second  maxilla  (X  4),  and  label:  winglike 
part,  gill  bailer,  shreds  of  muscle. 

9.  How  does  the  shape  of  the  gill  bailer  fit  it  for  the  work  it  does  ? 

E.    (Optional.)     Adaptations  for  food  getting. 

1.  Place  an  earthworm,  a  piece  of  beef,  or  a  piece  of  clam  near  a 
crayfish,  and  describe  the  way  in  which  he  gets  the 
food  to  his  mouth. 


156  ANIMAL   BIOLOGY 

2.  Of  what  use  may  the  mouth  parts  (easily  seen  in  a  living 

crayfish)  be  in  getting  food  into  the  mouth  ? 

3.  Push  the  outer  mouth  parts  of  a  living  crayfish  to  one  side 

with  the  forceps  and  find  a  pair  of  hard  jaws, 
mandibles.  Pry  them  open  a  little. 

a.  Do  they  work  from  side  to  side  or  up  and  down  ? 

b.  Describe  the  cutting  edges  of  the  mandibles. 

c.  Of  what  use  would  these  jaws  be  in  preparing  food  for 

swallowing  ? 

F.  (Optional.)     Adaptations  for  protection. 

1.  Describe  the  outer  covering  of  the  animal?     Of  what  use  is 

this  to  the  animal  ? 

2.  Locate  the  softer  parts  of  the  crayfish's  armor?    How  are 

these  protected  by  their  position  ? 

3.  Gently  touch  the  eye  of  a  living  crayfish. 

a.  Describe  the  movements  of  the  eye.     How  might  these 

movements  be  advantageous  to  the  animal  ? 

b.  Of  what  advantage  may  it  be  to  the  crayfish  to  have  its 

eyes  on  stalks  instead  of  on  the  surface  of  the  head  ? 

c.  Make  a  sketch  (X  4)  of  one  of  the  eyes  on  its  stalk. 

Label :  fleshy  stalk,  eye. 

4.  Of  what  use  may  the  large  pincers  be  in  addition  to  helping 

in  securing  food?  Sketch  (X  1)  one  of  the  large 
pincers  complete. 

G.  (Optional.)     Additional  drawings. 

1.  Make  out  the  parts  of  one  of  the  large  antennae.     Notice 

the  broad  finlike  part  at  the  base  of  the  antenna, 
then  two  segments,  and  a  long  lash  that  arises  from 
the  second  segment.  Sketch  (X2)  a  large  antenna. 
Label. 

2.  Make  a  sketch  (x  1)  of  dorsal  view  of  the  crayfish.     Label 

the  regions,  and  all  the  appendages. 

113.    Habits  of  crayfishes.  —  Crayfish  are  found  commonly 
throughout  the  United  States  in  rivers  and  their  tributaries 


CRAYFISHES  AND   THEIR  RELATIVES  157 

where  limestone  is  found,  since  lime  is  needed  in  making 
their  hard  outer  covering.  During  the  day  they  hide  under 
stones,  in  the  crevices  of  rocks,  in  the  mud,  and  sometimes 
in  specially  constructed  burrows  along  the  banks.  Since 
the  animal  backs  into  these  hiding  places,  its  big  claws  are 
ready  for  business  if  an  enemy  attacks  it. 

Then,  too,  the  colors  of  crayfishes  aid  somewhat  in  pro- 
tecting them  since  these  colors  are  usually  similar  to  the  color 
of  the  bottoms  of  the  streams  in  which  they  live.  Lastly, 
the  wide  range  of  vision,  which  the  stalked  eyes  afford  must 
serve  to  warn  the  animal  of  the  approach  of  danger.  Never- 
theless they  do  not  always  escape  since  crayfish  are  often 
captured  by  certain  birds  and  fishes.  In  fact,  crayfishes  are 
often  used  by  man  as  a  bait  for  catching  fishes. 

114.  Food,  food  getting,  and  digestion.  —  At  night  cray- 
fishes crawl  about  in  search  of  food,  concerning  which 
they  are  not  at  all  fastidious,  since  dead  fish  and  other 
dead  animals  seem  to  be  fully  as  acceptable  as  when 
alive.  In  fact,  they  are  natural  scavengers.  Crayfish 
seize  their  food  with  their  large  claws  and  with  the 
aid  of  the  small  pincers  on  the  front  walking  legs  and 
with  the  mouth  parts,  especially  the  mandibles,  reduce 
the  food  to  pieces  small  enough  to  be  eaten.  We  have  seen 
in  plants  (P.  B.,  63,  70,  71)  that  digestion  many  take  place  in 
any  living  cell  where  food  is  stored  or  manufactured.  Hence, 
plants  have  no  special  part  devoted  to  digestion.  In  cray- 
fishes, however,  it  is  quite  different,  since  a  part  of  the  body, 
known  as  a  digestive  system,  is  devoted*  to  preparing  the 
food  for  absorption  and  use.  This  digestive  system  consists 
of  a  food  tube  known  as  the  alimentary  canal  and  certain 
masses  of  cells  known  as  digestive  glands. 

After  the  food  is  digested,  it  can  pass  into  the  blood  by 


158  ANIMAL  BIOLOGY 

osmosis  and  be  carried  to  the  cells  1  of  the  body.  When  the 
digested  food  reaches  the  cells,  it  may  be  used  by  the  proto- 
plasm either  in  making  more  living  matter  or,  as  we  shall 
now  see,  for  the  release  of  energy. 

115.  Respiration  and  the  production  of  energy.  —  In  our 
laboratory  study  we  watched  the  movements  of  the  gill 
bailer  and  saw  that  it  caused  a  current  of  water  to  enter 
the  posterior  end  of  the  gill  chamber  and  flow  over  the  gills, 

thus  bringing  oxy- 
gen to  the  filaments 
(Fig.  111).  The 

gin  baiier  \         thin-walled     blood 

vessels  in  the  fila- 
ments absorb  the 
oxygen,  and  the 
blood  then  passes 

FIG.  111.  —  Gills  of  a  crayfish. 

on  into  other  blood 

vessels,  which  carry  it  back  to  the  heart,  whence  it  is  forced 
all  over  the  body  of  the  crayfish,  and  so  the  oxygen  in  the 
blood  passes  into  the  cells  as  does  the  food.  Now  what 
becomes  of  the  oxygen  ? 

As  in  plants  (P.  B.,  80),  the  oxygen  unites  with  ele- 
ments in  the  foods  and  protoplasm  of  the  cells  and  produces 
oxidation  and  liberation  of  energy,  which  gives  the  crayfish 
the  power  to  contract  its  muscles  and  so  push  against  the 
water  with  its  abdomen  and  tail  fin,  thus  propelling  the  animal 
backward,  or  to  open  its  nippers  and  shut  them  and  so  se- 
cure food.  In  fact,  all  the  work  that  the  crayfish  performs 
is  made  possible  through  the  burning  of  its  foods  or  proto- 
plasm by  the  oxygen. 

1  We  have  shown  in  plant  biology  (41)  that  plants  consist  of  cells 
which  are  largely  composed  of  living  matter  known  as  protoplasm. 
This  is  also  true  of  animals  (126). 


CRAYFISHES  AND   THEIR  RELATIVES  159 

Since  the  proteins,  fats,  carbohydrates,  and  protoplasm  all 
contain  carbon,  when  these  are  oxidized,  carbon  dioxid  (CO2) 
will  be  formed  as  one  of  the  waste  substances.  All  these 
waste  substances  will  pass  out  of  the  cells  into  the  blood, 
which  finally  conveys  them  to  the  filaments  of  the  gills. 
Here  the  waste  matters  pass  out  into  the  water,  which,  as  we 
have  seen,  is  then  forced  out  of  the  front  end  of  the  gill 
chamber. 

116.  Life  history.  —  As  in  the  seed-producing  plants, 
crayfishes  are  reproduced  by  means  of  special  cells  known  as 
egg-cells  which  in  crayfishes  are  formed  in  the  body  of  the  fe- 
male in  organs  known  as  ovaries.  Before  they  can  develop, 
however,  these  egg-cells,  as  in  the  seed  plants,  must  be  ferti- 
lized by  sperm-cells,  produced  in  spermaries  of  the  male  cray- 
fish. After  extrusion  the  fertilized  eggs  are  attached  by  a 
sticky  substance  to  small  appendages,  known  as  swimmerets, 
on  the  ventral  surface  of  the  abdomen  of  the  female  (Fig.  112). 
Here  the  fertilized  egg-cell  develops  into  a  many-celled  em- 
bryo, and  finally  a  tiny  crayfish  is  hatched.  At  first  the 
young  crayfishes  are  held  to  the  swimmerets  by  threads; 
later  they  cling  by  means  of  then*  pincers,  and  after  some 
days  become  independent.  At  intervals  in  both  young 
and  old  crayfishes,  the  hard  outer  covering  of  the  body 
is  shed.  This  shedding  of  the  skin  is  called  molting. 
But  for  this  process  it  would  be  impossible  for  the  young 
to  grow. 

While  the  young  crayfishes  are  attached  to  the  parent 
they  are  of  course  protected  by  their  position,  and  the  female 
looks  after  them  by  looking  out  for  herself.  The  food  for  the 
developing  embryo  is  stored  in  the  egg.  After  hatching,  the 
young  must  care  for  themselves,  and  after  they  become  in- 
dependent they  receive  no  protection  at  all.  There  is,  there- 


160 


ANIMAL  BIOLOGY 


fore,  in  the  case  of  crayfishes  nothing  like  the  parental  care 
of  higher  animals. 


FIG.  112.  —  Female  lobster  with  eggs  beneath  abdomen.     (Herrick's  "Amer- 
ican Lobster  "  —  United  States  Fish  Commission.) 


117.  Relatives  of  the  crayfish.  —  One  of  the  relatives  of  the  cray- 
fish is  the  lobster  (Fig.  112),  which  is  a  salt  water  animal  found  along 
the  north  Atlantic  coast.  Like  the  crayfish,  its  body  consists  of 


CRAYFISHES  AND   THEIR  RELATIVES 


161 


a  cephalothorax  and  a  clearly  segmented  abdomen.  The  lobster 
also  has  two  pairs  of  antennae,  a  pair  of  stalked  eyes,  a  number  of 
pairs  of  mouth  parts,  a  pair  of  big  claws,  four  pairs  of  walking  legs, 
to  the  bases  of  which  gills  are  attached,  and  a  pair  of  swimmerets 


abdomen 


FIG.  113. — The  crab. 


on  each  of  the  segments  of  the  abdomen  except  the  last.  In  general, 
lobsters  are  very  much  larger  than  crayfishes,  one  of  the  largest 
known  specimens  weighing  over  twenty-three  pounds. 

Less  like  the  crayfish  in  appearance  are  the  crabs,  yet  a  care- 
ful examination  shows  that  these  animals  have  practically  all  of 
the  characteristics  mentioned  hi  the  preceding  paragraph.  The 
cephalothorax  of  crabs,  however,  is 
usually  wider  than  it  is  long  (Fig. 
1 13) ,  and  the  abdomen  is  much  reduced 
and  is  commonly  folded  in  a  groove  be- 
neath the  cephalothorax.  Few  of  the 
crabs  are  able  to  swim ;  usually  they 
crawl  sideways  by  the  help  of  their 
four  pairs  of  walking  legs. 

"A  curious  modification  of  habit  is  shown  in  the  hermit  crab 
(Fig.  114),  which  in  early  life  backs  into  an  empty  snail  shell  which 
aids  in  protecting  it  from  its  enemies.  The  abdomen,  thus  covered, 
becomes  soft  and  flabby.  As  growth  proceeds  the  necessity  arises 
for  a  larger  shell,  and  the  crab  goes  '  house-hunting '  among  the  empty 
shells  along  the  shore,  or  it  may  forcibly  extract  the  snail  or  other 
hermit  from  the  home  which  strikes  its  fancy."  —  JORDAN  and 
HEATH,  "Animal  Forms." 

M 


FIG.   114.  — The  hermit   crab 
in  an  empty  snail  shell. 


162 


ANIMAL    BIOLOGY 


Among  the  relatives  of  the  crayfish  that  live  in  damp  places  on 
land  are  the  pill  bug  and  the  sow  bug  (Fig.  115)  which  are  often 
found  beneath  water-soaked  wood.  All  the 
animals  we  have  described  in  this  chapter 
belong  to  the  class  Crustacea,  so-called  from 
the  hard  outer  shell  which  invests  them. 

118.  Economic  importance  of  the  Crus- 
tacea.— Crayfishes  in  Europe,  particularly 
in  France,  are  highly  esteemed  as  food, 
and  special  efforts  are  made  to  increase 
their  number.  In  this  country,  however, 
they  have,  as  yet,  been  used  but  little  as 
food.  Their  principal  use  is  for  bait 
in  catching  certain  kinds  of  fish. 

The  lobster  is  to  us  what  the  crayfish 
is  to  Europeans.  While  they  are  not  abundant  enough  to 
be  considered  a  very  important  source  of  food,  still  the 
fishermen  in  1901  received  $1,400,000  for  the  lobsters 


FIG.   115.  — The    sow 
bug. 


FIG.  116. — The  shrimp. 


caught.  They  are  considered  rather  as  a  delicacy,  since 
they  are  too  expensive  for  general  use,  principally  on 
account  of  their  scarcity.  For  a  number  of  years  the 
United  States  government  has  been  making  efforts  to 
increase  the  number  of  lobsters  by  artificial  propagation. 
Some  states  have  passed  laws  forbidding  the  catching  of 
immature  lobsters  and  lobsters  with  eggs  attached. 


CRAYFISHES  AND   THEIR  RELATIVES  163 

Other  Crustacea  that  aret  used  for  food  are  prawns, 
shrimps  (Fig.  116),  and  certain  kinds  of  crabs.  Nearly 
all  the  Crustacea  eat  dead  animal  food ;  consequently 
they  are  useful  in  keeping  the  water  free  from  dead 
material. 


CHAPTER  VI 
PARAMECIUM  AND  ITS  RELATIVES 

119.   Study  of  the  paramecium.  —  Laboratory  study. 

Note  to  Teacher.  —  To  secure  paramecium  material,  add  some 
chopped  hay  to  a  large  jar  of  water  several  weeks  before  the  animals 
are  needed.  The  paramecia  develop  more  rapidly  and  are  of  larger 
size  if  the  water  is  secured  from  a  stagnant  pool.  The  hay  infusion 
furnishes  food  for  bacteria  upon  which  the  single-celled  animals 
feed.  To  obtain  the  paramecia,  transfer  to  a  glass  slide  with  a 
pipette  a  drop  from  near  the  surface  of  the  water. 

A.  General  appearance  of  paramecium. 

1.  Place  a  drop  of  water  containing  many  paramecia  or 

other  similar  forms  on  a  glass  slide  (with  concave 
depression  if  possible).  Examine  with  a  magni- 
fier. 

Describe  the    appearance  of   the   tiny   bodies   that 
you  see  moving  about. 

2.  Now  examine  the  drop  of  water  with  the  low  power 

of  the  compound  microscope.  Do  not  allow 
the  water  to  evaporate  entirely,  but  keep  adding 
a  little  from  time  to  time. 

a.  Do  the  paramecia  swim  slowly  or  rapidly  ? 

b.  Is  the  more  pointed  end  of  the  animal  usually 

foremost  in  swimming  or  the  rounded  end  ? 

B.  Structure  of  paramecium. 

Secure  a  stained  and  mounted   specimen  of 
a  paramecium,  or  add  a  drop  of  iodine  solution 
to  the  water  containing  the  living  animals,  and 
164 


PARAMECIUM  AND  ITS  RELATIVES  165 

place  a  cover  glass  on  top.  Examine  first  with 
the  low  power  of  the  microscope  and  then  with 
the  high  power.  Make  a  sketch  two  or  three 
inches  long  to  show  the  following :  — 

1.  The  general  shape  of  one  of  the  paramecia. 

2.  A  fringe  of  slender  hairlike   projections  around  the 

outer  surface.  They  are  called  cilia  (singular 
cilium,  from  Latin,  meaning  a  hair).  The 
cilia  are  projections  of  the  protoplasm  of  the 
cell.  They  project  from  the  upper  and  lower 
surface  also,  but  they  cannot  be  seen  readily. 

3.  A  more  deeply  stained  portion  of  the  protoplasm  near 

the  center,  the  nucleus  (Fig.  118).  The  rest 
of  the  cell  is  the  cell  body. 

4.  Particles  of  matter,  food  particles  scattered  through 

the  body  of  the  cell. 

5.  Label :  cilia,  nucleus,  food  particles,  cell  body. 

C.    Food  getting. 

To  the  drop  of  water  containing  the  living 
paramecia  add  a  little  finely  powdered  carmine, 
and  on  the  drop  place  a  cover  glass. 

1.  Tell  what  was  done. 

2.  Throw  all  the  light  you  can  on  the  paramecia  by 

means  of  the  mirror  and  use  the  larger  openings 
in  the  diaphragm.  What  evidence  have  you 
that  the  paramecia  are  feeding  on  the  carmine  ? 
Sometimes  it  is  necessary  to  leave  the  paramecia 
for  twenty-four  hours  before  they  feed. 

3.  Watch  the  paramecia  swimming  through  the  particles 

of  carmine.  What  evidence  have  you  that  the 
cilia  are  in  motion? 

4.  The  paramecium  has  &  furrow  on  one  side  of  its  body, 

and  from  the  furrow  a  tubular  passage  or  gullet 
leads  into  the  protoplasm.  Both  the  furrow 
and  the  gullet  are  lined  with  cilia. 

a.  If  you  are  able  to  see  either  the  furrow  or  the 

gullet,  describe  them. 

b.  In  what  direction  must  the  cilia  in  the  furrow  and 


166 


ANIMAL  BIOLOGY 


the  gullet  strike  the  swifter  and  with  the  more 
force  to  bring  food  particles  into  the  gullet  ? 

D.   Locomotion.     (Optional  demonstration.) 

Examine  with  a  high  power  a  paramecium  that  is 
comparatively  quiet.  Focus  carefully  and  look  for 
the  cilia. 

1.  Describe  the  cilia  and  their  movements. 

2.  When  the  paramecium  strikes  against  the  water  in  one  direc- 

tion, in  what  direction  would  its  body  tend  to 
move? 

Must  the  paramecium 
strike  harder 
toward  the 
blunt  end  or 


3. 


toward 
pointed 
when 
swims 


the 

end 

'it 

with 


E. 


the  blunt  end 
foremost  ? 

Excretion  of  liquid  waste. 

(Optional  demonstration.) 

Look  at  a 


mouth 


contractile 
vacuole 

gullet  with 
food  ball 


large  nucleus 
•small  nucleus 


'food  balls 


paramecium 

or   vorticella 

with  both  the 

low  and  high 

power  and 

search  for 

clear  circular 

spots.  Watch 

to  see  if  any 

of  these  contract. '   If  they  do,  they  are  contractile 

vacuoles.    There  are  two  in  paramecium  and  one 


B,  vorticella 
FIG.  117.  —  Protozoa  with  cilia. 


PARAMECIUM  AND  ITS  RELATIVES 


167 


in  vorticella  (Fig.  117).  The  liquid  waste  flows 
from  the  protoplasm  into  these  spaces,  the  pro- 
toplasm then  pushes  together  and  forces  the 
waste  out  of  the  body. 

1.  Describe  the  position,  appearance,  and  action  of  the  con- 

tractile vacuoles. 

2.  State  in  your  own  words  the  use  of  the  contractile  vacuoles. 

3.  Sketch  the  contractile  vacuoles  in  your  drawing  of  the  para- 

mecium  and  label. 

F.   Reproduction  of  paramecium.     (Optional  demonstration.) 

All  the  time  while  you  are  studying  the  parame- 
cium be  on  the  lookout  for  forms  that  are  dividing. 
If  you  do  not  see  any,  examine  mounted  slides  that 
show  the  paramecium  dividing.  Make  a  sketch 
three  inches  long  of  a  paramecium  dividing,  to  show 
--how  it  reproduces. 

120.  External  structure  and  locomotion.  —  In  form  a 
paramecium  resembles  somewhat  the  shape  of  a  slipper, 
hence  it  is  sometimes  called  the  "slipper-animal"  (Fig.  118). 


contract//*  vacoole 


food  vacuoles  t,f 

/     ^  confracMe  vacuofe 


cilia  — 


nucleus 


FIG.  118. — The  paramecium.     (Dahlgren.) 

Extending  from  all  parts  of  its  outer  surface  are  many  tiny 
projections  of  protoplasm  that  look  like  colorless  hairs; 
these  are  known  as  cilia  (singular  cilium).  In  locomotion 


168  ANIMAL  BIOLOGY 

the  animal  usually  moves  with  the  blunt  end  (i.e.  heel  of  the 
slipper)  in  front,  the  paramecium  being  propelled  by  the 
strong  backward  strokes  of  the  cilia  and  a  slower  recovery. 
When  it  runs  into  an  obstacle,  the  cilia  are  reversed  in  action 
and  thus  the  animal  is  enabled  to  move  with  the  opposite  end 
(toe  of  slipper)  in  front.  Most  animals  that  swim  (e.g.  fishes 
and  frogs)  have  broad  and  flat  appendages  which  are  com- 
paratively large.  In  paramecium,  on  the  other  hand,  the 
organs  of  locomotion  (cilia),  while  slender,  are  so  numerous 
that  they  perhaps  accomplish  the  same  results  as  the  broad 
swimming  appendages  of  the  frogs  and  fishes. 

121.  Food,  food  getting,  and  digestion.  —  Paramecia  feed 
upon  one-celled  plants  and  animals.     On  one  side  of  a  para- 
mecium is  a  furrow  or  groove,  which  is  lined  with  cilia.    At  the 
lower  end  of  the  groove  is  an  opening,  the  mouth,  which  leads 
into  a  short,  tubular  gullet.     The  rapid  motion  of  the  cilia 
in  the  groove  draws  the  food  toward  the  mouth  opening  and 
other  cilia  lining  the  gullet  push  down  the  food  particles. 
Small  collections  of  these  food  particles  are  made  at  the  lower 
end  of  the  gullet,  and  these  masses,  food  balls,  are  circulated 
within  the  cell  by  the  streaming  movement  of  the  proto- 
plasm.    Although  the  paramecium  is  a  single  cell,  it  has  cer- 
tain parts  specially  developed  for  securing  food,  just  as  the 
higher  animals  have  special  organs  for  this  function. 

As  the  food  balls  circulate  through  the  protoplasm,  they 
are  gradually  digested,  and  the  food  materials  thus  liquefied 
are  used  as  in  plants  and  other  animals  for  the  production 
of  more  protoplasm  or  for  the  release  of  the  energy  needed 
for  locomotion  and  for  food  getting.  The  indigestible  parts 
of  food  are  forced  out  through  the  side  of  the  body. 

122.  Respiration    and    the    liberation    of    energy.  —  The 
paramecium  is  surrounded  by  water  that  contains  oxygen 


PARAMECIUM  AND  ITS  RELATIVES 


169 


and  this  passes  into  the  protoplasm  through  the  thin  mem- 
brane surrounding  the  animal.  When  the  oxygen  combines 
with  the  chemical  elements  found  in  foods  and  protoplasm, 
oxidation  is  carried  on,  energy  is  released,  and  waste  sub- 
stances are  formed  which  are  given  off  in  the  process  of 
excretion. 


123.  Excretion  of  wastes. — At  either  end  of  the  animal 
is  a  clear  space  which  is  sometimes  circular  and  at  other  times 
star-shaped.     These  are  the  contractile  vacuoks.     The  wastes 
formed  by  oxidation  (e.g.  carbon  dioxid  and  water)  collect 
to  form  the  vacuoles.     The  protoplasm  presses   upon  the 
waste  materials  and  periodically  squeezes  them  out  of  the 
animal.    When  this  occurs,  the  contractile  vacuole  disappears. 

124.  Reproduction  and  life  history.  —  In  the  interior  of  a 
paramecium  are  two  nuclei  known  as  the  large  nucleus  and 
the  small  nucleus,  both  of  which 

show  readily  when  the  animal  is 
stained  with  iodine  or  with  other 
chemicals.     When  the   animal  re- 
produces, both  the  large  and  small 
nuclei  divide  in  halves  (Fig.  119), 
a  new  mouth  and  gullet  are  formed,    smal, 
and  two  new  contractile  vacuoles    nucleus 
appear.     The   cell   body  then  di- 
vides transversely,  the  cells  sepa- 
rate  from   each   other,   and  thus 
from  a  single  individual,  two  new 
paramecia  are  formed.     If  condi- 
tions are  favorable,  both  animals 
grow  and  may  in  turn  reproduce  at  the  end  of  twenty- 
four  hours.     "It  has  been  estimated  that  one  paramecium 


mouth  -  - 


mouth 


large 
nucleus 


FIG.  119.  —  A  paramecium  di- 
viding. 


170  ANIMAL  BIOLOGY 

may   be    responsible    for    the    production    of    268,000,000 
offspring  in  one  month." 

125.    Study  of  amoeba  (plural,  amoebae  or  amoebas). —  (Optional 
laboratory  study.) 

A.  Structure  of  amoeba. 

Examine  a  living  amoeba  or  a  stained  specimen  on  a  pre- 
pared slide.  Use  a  low  power  of  the  compound  microscope 
at  first,  and  then  as  high  a  power  as  may  be  neces- 
sary. Make  a  sketch  about  three  inches  long  to  show 
the  following :  — 

1.  An  outline  to  show  the  shape  of  the  animal,  including  any 

projections  of  the  protoplasm,  which  are  called  pseudopods 
(Greek  pseudo  =  false  +  pod  =  foot ;  hence,  the  name 
false  foot). 

2.  The  main  mass  of  the  amoeba,  clear  and  jellylike  in  a  living 

amoeba,  slightly  stained  in  a  mounted  specimen,  which 
is  called  the  cell  body. 

3.  A  slightly  denser  part  of  the  protoplasm  in  the  living  form  or 

stained  much  darker  in  the  preserved  animal,  the  nucleus. 

4.  Particles  of  food  or  one-celled  plants  scattered  through  the 

cell  body. 

5.  Label :    false  feet  or  pseudopods,  nucleus,  cell  body,  food 

particles. 

6.  If  time  allows,  draw  several  different  forms  assumed  by  the 

specimen. 

B.  Locomotion. 

In  a  living  amoeba  watch  with  the  high  power  of  the 
microscope  the  creeping  movements,  and  the  projections 
of  the  pseudopods. 

1.  Are  the  movements  slow  or  rapid  ? 

2.  In  your  own  words  give  a  description  of  the  locomotion  of 

the  amoeba. 


PAEAMECIUM  AND  ITS  RELATIVES 


171 


C.   Excretion  of  liquid  waste. 

Look  for  a  clear,  roundish  spot  in  the  amoeba  which  at 
intervals  disappears.  This  is  the  contractile  vacuole. 
The  liquid  waste  flows  into  this  space  and  then  the 
protoplasm  pushes  together  and  forces  the  waste  out  of 
the  body. 

1.  Describe  in  your  own  words  the  appearance  and  action  of 

the  contractile  vacuole. 

2.  Sketch  the  contractile  vacuole  in  your  drawing  of  the  amoeba 

and  label. 

126.  A  comparison  of  paramecium  and  amreba.  —  Both  amoeba 
and  paramecium  are  animals  so  small  that  they  can  barely  be  seen 
with  the  naked  eye. 
Both  live  in  water, 
both  are  one-celled 
and 
the 


both 


annuals, 

carry  on  tne  same 
functions,  but  in  a 
somewhat  different 
manner.  While  the 
paramecium  main- 
tains a  more  or  less 
fixed  form,  the 
amoeba  is  capable 
of  assuming  almost 
any  shape  (Fig.  120). 
This  it  does  by  caus- 
ing portions  of  its 
substance  to  flow  out  in  many  directions.  These  projections 
are  known  as  pseudopods  which  mean  false  feet.  By  pushing 
out  these  pseudopods  in  front  and  pulling  up  its  protoplasm 
from  behind,  the  amoeba  slowly  flows  from  one  part  of  the  slide 
to  another. 

Unlike  the  paramecium  an  amoeba  has  no  definite  part  of  the 

When  the  animal  is  feeding, 


pseudopod 
FIG.  120.  —  The  amoeba. 


body  through  which  it  takes  in  food. 


172  ANIMAL  BIOLOGY 

it  slowly  flows  about  the  one-celled  plant  or  animal  and  finally 
ingulfs  it.  The  processes  of  digestion,  assimilation,  respiration, 
excretion,  and  reproduction  (Fig.  121)  are  much  the  same  in  amceba 
as  in  paramecium.  Both  these  animals  belong  to  a  group  of  animals 
known  as  the  Protozoa  (Greek  protos  =  first  or  simplest  +  zoon  = 
animal) . 


FIG.  121.  —  An  amoeba  dividing. 

127.  To  show  that  the  higher  animals  are  composed  of 
many  cells.  —  Laboratory  study. 

Frogs  are  continually  shedding  parts  of  their  epidermis, 
and  pieces  of  this  thin  membrane  are  likely  to  be  seen  cling- 
ing to  a  frog  in  an  aquarium  or  floating  in  the  water.  Secure 
a  piece  of  this  membrane,  spread  it  on  a  slide,  add  a  drop 
of  water  and  a  cover  glass,  and  examine  with  the  low  power 
of  the  microscope. 

1.  Describe  the  form  and  color  of  each  cell. 

2.  In  each  cell  notice  a  body,  usually  near  the  center  and 

slightly  more  dense  than  the  rest  of  the  cell.     This  is 
the  cell  nucleus.     (If  the  nucleus   does  not  show 
clearly,  add  a  drop  of  iodine  to  the  membrane.) 
The  rest  of  the  cell  is  the  cell  body. 
a.   Name,  now,  two  parts  of  a  cell  of  the  frog's  epidermis. 


PAEAMECIUM  AND  ITS  RELATIVES  173 

6.   State  the  form  and  position  of  the  cell  nucleus. 
3.   Make  a  drawing  of  three  of  the  cells  described  above, 
each  cell  to  be  represented  about  an  inch  in  diameter. 
Label  cell  body  and  cell  nucleus. 

4.  (Optional.)  Demonstrate  by  the  use  of  prepared  slides, 
pictures,  or  charts  that  the  blood,  intestine,  and  other 
organs  of  the  body  of  a  frogr  or  other  higher  animal  are 
composed  of  cells.  Make  a  drawing  of  a  single  cell  in 
each  case. 

128.  A  comparison  of  Protozoa  and  the  higher  animals.  - 
Our  study  thus  far  has  shown  that  all  animals,  including  the 
Protozoa,  perform  the  necessary  functions  of  locomotion, 
food   getting,  assimilation,  respiration,    and    reproduction. 
The  adaptations  for  performing  these  functions,  however, 
are  very  diverse. 

All  animals  except  the  Protozoa  consist  of  many  cells  and 
the  various  functions  of  the  higher  animals  are  performed  by 
groups  of  cells  known  as  organs.  For  example,  certain  com- 
binations of  cells  carry  on  locomotion,  others  digestion,  while 
still  others  are  set  apart  for  breathing.  All  these  functions 
are  performed  in  a  Protozoan  by  a  single  cell. 

129.  Economic  importance   of  Protozoa.  —  Most  of  the 
Protozoa  serve  as  food  for  other  animals  that  live  in  the 
water  and  these  in  turn  are  fed  upon  by  fish,  which  are  eaten 
by  man.     Thus  the  one-celled  plants  and  animals  are  found 
to  be  an  important  food-basis  for  human  beings. 

Some  of  the  Protozoa  that  live  in  the  sea  secrete  tiny  shells 
(Fig.  122),  and  when  the  animals  die  the  shells  drop  to  the 
bottom.  As  a  result  of  heat,  pressure,  and  other  causes, 
this  bottom  ooze  is  gradually  solidified  to  form  chalky 
rocks,  and  in  the  upheavals  that  have  taken  place  in  ages 
past  these  rocks  have  been  forced  above  sea  level.  The 


174 


ANIMAL  BIOLOGY 


chalk  cliffs  of  Dover,  England,  were   doubtless  formed  in 

this  way. 

While  most  of  the  Protozoa  are  harmless,  there  are  a  few 

forms  that  have  become  para- 
sitic in  human  beings.  We 
have  already  discussed  the 
single-celled  animal  that 
causes  malaria  and  that  is 
carried  from  one  individual 
to  another  by  the  Anopheles 
mosquito  (39).  This  parasite 
resembles  an  amoeba  in  form. 
Another  form  of  Protozoan 


FIG.  122.  —  The  shells  of  one-celled 
animals  as  they  are  found  in  chalk. 
(Scott,  Geological  Survey  of  Iowa.) 


causes  the  terrible  disease 
known  as  the  sleeping  sick- 
ness of  tropical  Africa.  Many 
biologists  believe  that  yellow  fever  (41)  is  caused  by  a 
protozoan  that  is  transmitted  by  the  Stegomyia  mosquito. 


CHAPTER  VII 


ADDITIONAL   ANIMAL    STUDIES 
A.   Porifera  (sponges) 

130.  Sponges.  —  The  sponges  are  animals  more  complex  in 
structure  than  the  Protozoa,  for  they  are  composed  of  many  cells ; 
nevertheless,  they  are  comparatively  simple  in  structure  since  they 
have  no  digestive,  circulatory,  respiratory,  or  nervous  system,  and 
therefore  each  cell  has  to  carry  on  practically  all  the  necessary 
nutritive  functions. 

Sponges  differ  largely  in  the  kind  of  skeletons  that  they  possess. 
In  the  common  bath  sponge  (Fig.  123)  this  is  composed  of  a  tough, 
horny  material.  When 
sponges  are  ready  for  market, 
only  the  horny  skeleton  re- 
mains, the  living  cells  hav- 
ing been  killed  and  removed. 
The  sponge  skeleton  shows 
a  large  number  of  pores  in 
the  outer  surface,  and  for 
this  reason  the  name  Porifera 
(Latin  =  pore-bearing)  is 
given  to  this  group  of  ani- 
mals. The  pores  lead  into 


FIG.  123.  — Bath  sponge. 


canals  that  run  through  the  body,  finally  connecting  with  one  or 
more  larger  central  cavities  that  lead  outward,  usually  at  the  top. 
In  certain  parts  of  these  canals  there  are  cells  with  cilia;  their 
action  causes  water  to  rush  into  the  canals  through  the  pores, 
bringing  food  and  oxygen  to  all  the  cells  of  which  the  sponge  is 

175 


176 


ANIMAL   BIOLOGY 


composed.  The  wastes  are  forced  out  through  the  larger  canals 
referred  to  above.  Like  the  bath  sponge,  all  other  Porifera  are 
stationary  in  their  mature  form. 


B.    Ccelenterata 

131.  Hydra.  —  A  study  of  a  fresh  water  coelenterate  known  as 
hydra  will  give  one  a  fair  idea  of  the  structure  and  adaptations  of 
this  group  of  animals.  Hydra  is  a  small  animal  found  in  fresh  water 
attached  to  water  plants,  and  sometimes  to  surfaces  of  stones  or 


tentacle" 
nettling  cells 


young  sperm-cells 

digestive  cavity "J, 

mature  egg  — 


embryo 
hydras  \ 


mature 
sperm-cells 


i__  young 
tentacle 


bud 


young  egg 


base  of  hydra 
FIG.  124.  —  Longitudinal  section  of  a  hydra.     (Hegnejc.) 

other  objects  on  the  bottom.  At  the  upper  end  of  the  tiny  cylin- 
drical column  are  threadlike  bodies  known  as  tentacles  (Fig.  125,  1). 
If  the  animal  is  touched  with  a  needle  or  pencil,  it  contracts  its 
body  and  tentacles  so  much  that  it  can  scarcely  be  seen.  But  in  a 
short  time  it  expands  again. 

If  the  hydra  happens  to  be  hungry  and  some  small  form  of  animal 


ADDITIONAL  ANIMAL   STUDIES 


111 


comes  in  contact  with  the  waving  tentacles,  the  hydra  ejects  micro- 
scopic threads  from  certain  cells  (nettling  cells)  in  the  tentacles. 
The  animal  thus  attacked  is  benumbed,  and  the  hydra  then  uses 
the  tentacles  to  push  its  prey  into  a  mouth  epening  in  the  center 
of  the  circular  row  of  tentacles.  The  food  is  drawn  into  the  inside 
of  the  column,  which  is  simply  a  hollow  tube  (Fig.  124).  Here 
certain  cells  secrete  digestive  fer- 
ments which  dissolve  the  foods  that 
the  animal  has  eaten,  and  the  indi- 
gestible matter  is  ejected  from  the 
mouth.  The  digested  food  is  then 
absorbed  by  the  cells  lining  the 
cavity.  Since  the  animal  is  bathed 
outside  and  inside  by  water  contain- 
ing oxygen,  the  cells  are  able  to 
absorb  oxygen  from  the  water  and 
to  give  off  carbon  dioxid  to  the 
water.  Hence  no  breathing  organs 
are  needed. 

It  is  evident  that  the  tentacles 
with  the  nettling  cells  also  serve  to 
protect  the  hydra  from  too  great 
familiarity  on  the  part  of  visitors 
that  might  otherwise  use  it  for  food. 
When  the  hydra  moves  from  one 
place  to  another,  it  bends  over 


FIG.  125.  — The  movements  made 
by  hydra  in  locomotion.  (Jen- 
nings.) 


until  the  ends  of  the  tentacles  touch  the  surface  on  which  it  rests. 
The  tentacles  then  adhere  to  this  surface,  the  bottom  of  the 
column  lets  go,  and  the  animal  turns  a  somersault  (Fig.  125)  and 
lands  on  the  lower  part  of  the  column ;  the  process  may  then  be 
again  repeated. 

Like  the  higher  animals  the  hydra  reproduces  by  means  of  eggs 
and  sperms.  But  it  also  has  another  interesting  way  of  producing 
new  individuals.  On  the  surface  of  the  column  one  frequently  sees 
little  bunches.  These  are  called  buds  (Fig.  124).  They  keep  on 
growing  outward  till  at  last  little  tentacles  and  a  mouth  opening  are 


178 


ANIMAL  BIOLOGY 


formed  at  the  tip  of  each.  It  is  now  evident  that  we  are  looking  at  a 
very  tiny  hydra.  Finally  the  new  individuals  separate  from  the 
column  and  begin  an  independent  life.  This  method  of  reproduc- 
tion is  known  as  budding. 


A,  organ-pipe  coral  B,  precious  coral 

FIG.  126.  —  Different  forms  of  coral. 


C,  sea-feather 


132.  Suggestions  for  the  study  of  hydra.  —  Laboratory  study. 
Pupils  should  be  supplied  with  living  hydra  if  possible.  The  column 
and  tentacles  should  be  observed  by  the  aid  of  a  magnifier,  described 

and  drawn.  The  animal 
should  be  touched  and  the 
action  of  the  column  and 
tentacles  noted  and  de- 
scribed. If  the  hydra  moves 
from  place  to  place,  the 
method  of  locomotion 
should  also  be  described. 


FIG.  127.  —  Jellyfish.     (Hargitt.) 


133.  Relatives  of  hydra. 
—  Among  the  relatives  of 
hydra  are  the  corals  (Fig.  126),  sea-anemones,  and  jellyfish  (Fig. 
127).  One  form  of  coral,  the  red  coral,  is  of  considerable  economic 
importance.  In  all  the  corals  the  column  secretes  a  mineral  sub- 


ADDITIONAL  ANIMAL  STUDIES  179 

stance  within  which  the  animal  can  withdraw  when  danger 
threatens.  In  the  case  of  the  red  coral  this  material  is  horny.  It 
is  used  for  decoration,  and  some  communities  on  the  Mediterranean 
are  devoted  largely  to  the  gathering  of  this  coral,  and  to  making 
it  into  various  forms  of  jewelry. 

C.   Annelida 

134.  Earthworm.  —  The  most  common  representative  of  the 
annelida  is  the  earthworm  (Fig.  128).  The  general  form  of  this  ani- 
mal is  long  and  cylindrical.  If  one  places  an  eartftsvorm  on  the 


\--Moutrt 

"Excretory 
opemrr§s 

FIG.  128.  —  The  earthworm.     (Sedgwick  and  Wilson.) 

ground,  it  will  start  to  crawl  away  or  bore  into  the  soil.  Observe 
that  the  end  that  is  foremost  is  tapering.  This  is  the  anterior  end. 
The  opposite  or  posterior  end  is  broader  and  considerably  flattened. 
The  part  of  the  body  on  which  the  worm  crawls  is  the  ventral  sur- 
face, which  is  somewhat  flattened,  while  the  dorsal  surface  is  rounded. 
The  whole  body  is  composed  of  rings  or  segments.  About  one  third 
of  the  distance  from  the  anterior  end  of  the  worm  several  of  the  seg- 
ments are  usually  somewhat  enlarged  and  form  the  girdle. 

At  the  anterior  end  toward  the  ventral  surface,  there  is  a  small 
opening.  This  is  the  mouth,  and  through  it  the  earthworm  sucks 
in  its  food  which  consists  not  only  of  dirt,  but  of  leaves  of  various 
kinds.  Overhanging  the  mouth  is  a  tiny  projection,  the  lip.  The 
animal  has  no  special  breathing  organs.  The  skin,  however,  is 
permeated  with  capillaries,  and  thus  serves  as  a  breathing  organ. 

Locomotion  is  brought  about  by  alternately  lengthening  and  then 


180  ANIMAL  BIOLOGY 

shortening  one  portion  of  the  body  after  another.  On  the  ventral 
region  of  the  body  are  rows  of  bristles  which  aid  in  locomotion.  The 
bristles  project  backward  when  the  worm  is  moving  forward,  and 
so  keep  the  animal  from  slipping  backward  when  it  lengthens  itself. 
The  bristles  also  serve  to  hold  the  animal  in  its  burrow. 

Earthworms  are  of  considerable  value  in  the  soil.  They  burrow 
through  the  earth  by  swallowing  the  dirt  which  is  mixed  with  vege- 
table matter;  both  are  then  acted  upon  by  digestive  juices  in  the 
alimentary  canal.  The  refuse  of  the  food,  which  is  not  available 
for  use  in  the  body,  is  ejected  from  the  posterior  end  of  the  intestine. 
The  little  piles  of  dirt  that  are  sometimes  so  common  on  a  lawn  are 
the  "  castings  "  of  earthworms.  It  has  been  found  that  soil  worked 
over  by  these  animals  is  in  better  condition  for  the  growth  of  plants. 
Then,  too,  the  deeper  soil  that  has  not  been  used  by  plants  is  brought 
to  the  surface  and  mingled  with  the  dirt  recently  used.  Darwin  1 
estimated  that  in  England  earthworms  annually  bring  to  the  top  of 
the  ground  eighteen  tons  of  soil  per  acre. 

135.  Suggestions  for  the  study  of  the  earthworm.  —  Laboratory 
study. 

This  study  should  be  made  upon  living  worms.  The  pupil 
should  first  note  and  describe  the  general  shape  and  segmentation 
of  the  animal,  the  differences  between  the  anterior  and  posterior 
ends,  the  dorsal  and  ventral  surfaces,  and  the  characteristic  appear- 
ance of  the  girdle.  An  earthworm  should  be  placed  on  a  moist 
surface  such  as  soil  or  wet  paper,  and  the  locomotion  of  the  animal 
observed  and  described.  A  large  specimen  should  be  pulled,  an- 
terior end  first,  between  the  fingers,  and  the  action  of  the  bristles 
noted  and  their  situation  and  appearance  studied  with  the  help  of 
a  magnifier.  Touch  the  earthworm  on  various  parts  of  the  body, 
and.  determine,  if  possible,  which  portions  are  the  most  sensitive. 
Look  on  the  dorsal  and  ventral  surfaces  for  blood  vessels,  and  watch 
the  pulsations  of  the  blood  in  these  vessels ;  describe  the  location  of 
these  blood  vessels  and  state  the  direction  in  which  blood  flows  in 
each  of  them. 

Darwin's  "Vegetable  Mold  and  Earthworms." 


ADDITIONAL  ANIMAL    STUDIES 


181 


136.  Relatives  of  the  earthworm.  —  Two  forms  of  animals  that 
formerly  were  classed  with  the  earthworm  under  the  head  of  "  worms  " 
are  the  tapeworm  (Fig.  129)  and  trichina.  The  tape  worm  is  some- 
times present  in  beef  and  trichina 
(Fig.  130)  in  pork.  Meats,  there- 
fore, should  be  well  cooked  to  kill 
all  such  parasites.  The  trichina,  if 
it  gets  into  the  human  system, 
causes  great  suffering.  When  a 
tapeworm  becomes  attached  to  the 
human  intestine  by  the  suckers  and 
hooks  on  its  anterior  end,  it  is  diffi- 
cult to  dislodge. 

D.   Mollusca 


137.  Fresh  water  mussel.  —  The 
fresh  water  mussels  are  mollusks 
that  are  sometimes  called  clams. 
They  are  often  quite  abundant  on 
the  bottom  of  'creeks, 
rivers,  ponds,  or  lakes. 
Usually  they  are  partly 
covered  with  sand  or 
mud,  sometimes  even 
more  than  is  shown  in 
Figure  131.  It  will  be 
seen  at  once  that  the 
mussel  is  inclosed  by  a 


B,  tapeworm,    about  15  feet  long, 
omitted  portions  being  indicated 


FIG. 


129. —  The  tapeworm. 
MacBride.) 


(Shipley  and 


shell.  This  consists  of 
two  parts  called  valves; 
hence  these  animals,  as  well  as  salt  water  mussels,  clams,  and 
oysters  are  called  bivalves  (Latin  bis  =  two  +  valve).  The  two 
valves  are  held  together  along  one  margin  by  a  tough  material 
that  serves  as  a  hinge.  On  each  valve  near  the  hinge,  a  promi- 
nence, known  as  the  beak  or  umbo,  may  be  readily  seen.  Around 


182 


ANIMAL  BIOLOGY 


the  umbo,  in  ever  widening  concentric  rings,  are  the  lines  of  growth 
of  the  animal,  which  indicate  younger  stages  in  its  development. 

Let  us  now  pull  up  a  mussel  and  lay  it  on  a  sandy  bottom.  In  a 
few  moments  the  shell  will  open  somewhat  and  from  one  end  will 
project  a  pinkish  body,  which  may  finally  extend  some  distance. 

This  organ  is  the  foot.  If 
we  watch  long  enough,  we 
may  see  the  mussel  use  the 
foot  to  push  itself  over  the 
surface  of  the  sand  or  it 
may  burrow  into  the  sand, 
and  finally  come  to  occupy 
a  position  like  that  in 
which  we  found  it. 


FIG.  130.  —  Trichina  in  Muscle.    (Leuckart.) 


exhalent  siphon 


Now  if  one  is  patient,  and  the  animal  feels  at  home,  it  will  be  pos- 
sible to  see  the  method  of  eating  and  breathing.  At  the  end  oppo- 
site the  foot  there  may  slightly  project  from  the  shell  a  fringed  and 
somewhat  tubular-shaped  structure.  Let  us  place  a  little  finely 
powdered  carmine  in  the  water  above  the 
opening.  As  the  carmine  slowly  sinks 
and  comes  opposite  the  tube,  the  particles 
will  suddenly  be  drawn  into  the  tube.  This 
shows  that  water  is  being  sucked  into  the 
tube,  and  it  brings  with  it  oxygen  and 
any  food  that  may  be  near,  such  as  mi- 
croscopic plants  and  animals. 

To  learn  any  more  about  the  feeding 
and  breathing  of  the  mussel  it  will  be  neces- 
sary to  open  the  shell.  Let  us  take  an- 
other mollusk  and  pry  open  the  valves. 
We  shall  soon  find  that  this  is  not  easy  to  do.  The  reason  will  be 
evident  after  studying  Figure  132. 

The  valves  are  held  together  by  strong  muscles.  So  we  pry  the 
valves  open  a  little  with  a  heavy  knife  and  then  slip  another 
sharp  knife  in  close  to  the  valve,  where  we  meet  an  obstruction 
toward  one  end.  When  we  have  cut  this,  the  valve  opens  at  that 


foot 


FIG.  131.  — Mussel  bur- 
rowing in  sand. 


ADDITIONAL   ANIMAL   STUDIES 


183 


end.  After  cutting  the  muscle  at  the  other  end,  we  can  readily 
separate  the  valves.  All  over  the  surface  of  the  animal,  except 
where  the  two  muscles  were  attached  to  the  shell,  is  a  thin  cover- 
ing called  the  mantle.  By  raising  the  body  of  the  mussel  from  the 
valve  it  will  be  evident  that  there  is  a  similar  structure  on  the 
other  side. 

Now,  if  we  fold  back  the  mantle,  it  will  be  possible  to  follow  the 
course  of  the  food  and  water.     The  first  thing  that  strikes  our  at- 


muscles  that  hold 
the  valves  to- 
gether 


umbo 


muscles        that   . 
hold  the  valves    \ 
together 


excurrent  siphon 


incurrent 
siphon 


lines  of  growth 
FIG.  132.  —  Fresh  water  mussel  with  foot  extended. 

tention  is  the  contracted  foot,  and  above  this  is  a  soft  mass  called 
the  abdomen.  In  the  abdomen  are  found  the  digestive  organs.  On 
each  side  of  the  abdomen  are  two  broad,  thin  flaps,  the  gills,  by  which 
the  animal  breathes.  Between  the  foot  and  the  end  that  was  bur- 
ied in  the  sand  are  found,  on  either  side  of  the  body,  two  small  flaps 
or  palps,  and  between  them  lies  the  mouth  opening.  To  this  mouth 
the  food  that  has  been  swept  into  the  tube  is  brought  by  the  wav- 
ing of  thousands  of  cilia  that  are  found  on  the  surface  cells  of  the 
gills  and  palps. 

Let  us  now  return  to  the  study  of  the  mussel  partly  covered  by 
the  sand.  The  hinge  is  on  the  dorsal  region  of  the  body,  the  free 
edges  of  the  valves  on  the  ventral,  while  the  mouth  and  foot  are  at 


184  ANIMAL   BIOLOGY 

the  anterior  end.  Hence,  the  animal  in  its  natural  position  "stands 
on  its  head,"  or  at  least  where  its  head  ought  to  be.  From  the  pos- 
terior end  projects  the  tubular  structure  to  which  reference  has  been 
made. 

Let  us  again  drop  some  powdered  carmine  closer  to  the  animal, 
and  watch  the  particles  when  they  reach  a  point  just  above  the  tube 
where  we  saw  the  particles  enter.  We  shall  now  see  the  carmine 
carried  away  from  the  animal  instead  of  into  it.  A  closer  examina- 
tion reveals  the  fact  that  the  tubular  structure  has  a  secqnd  opening 
above  the  first.  Both  of  these  tubes  are  called  siphons,  the  lower 
being  the  incurrent  siphon,  and  the  upper  the  excurrent  siphon. 
The  stream  of  water  forced  out  of  the  excurrent  siphon  carries  with 
it  the  carbon  dioxid  and  other  wastes  of  the  body. 

138.  Suggestions  for  study  of  the  mussel.  —  It  is  desirable  to 
have  students  see  the  mussel  in  its  natural  home.     They  should 
tell  where  they  found  the  animals  and  the  positions  in  which  they 
were  seen.     It  would  then  be  well  for  the  pupil   to  study  in  the 
laboratory  the  shell,  making  out  the  points  of  structure  described 
above.       A  drawing  of    a    side  view  of    the  mussel  should    be 
made    and    labeled    as    follows :    valve,    umbo,    hinge,    lines    of 
growth,    anterior    region,    posterior   region,   dorsal   edge,    ventral 
edge.     It  is  also  desirable  that  a  drawing  of  the  animal  in  the 
sand  or  mud  be  made  and  the  incurrent  and  excurrent  siphon 
openings  be  labeled. 

The  pupil  might  well  follow  the  account  as  given  above,  verifying 
the  statements  and  experiments,  and  making  drawings  of  the  mussel 
with  the  shell  open  and  all  the  animal  lying  in  one  valve.  Label: 
mantle,  muscles  that  close  shell,  incurrent  siphon,  excurrent  siphon, 
Also  a  drawing  should  be  made  of  the  muksel  with  the  mantle  re- 
moved. Label:  foot,  abdomen,  palps,  mouth,  gills.  Write  an 
account  of  how  the  mussel  moves  or  burrows,  how  it  feeds  and 
breathes. 

139.  Relatives  of  the  mussel.  —  Some  of  the  relatives  of  the 
mussel  are  the  clams,  oysters,  salt  water  mussels,  snails  (Fig.  133), 
and  slugs.     While  the  fresh  water  mussels  are  not  much  used  for 


ADDITIONAL  ANIMAL   STUDIES  185 

food,  they  are  important  economically  on  account  of  the  pearly 
matter  that  is  found  on  the  inside  of  their  shells.  This  is  used  in 
making  buttons  and  other  articles.  In  fact,  there  is  a  considerable 
industry  in  this  line 
along  the  Missis- 
sippi River.  $y  J  JH3^  _._  /  feeler 

Oysters  are  im- 
portant as  an  arti- 
cle of  food.  The 
oyster  fishermen  re- 
ceive annually  from 
twenty  to  thirty  mil-  FIG  13°°_  The  gnail 

lions  of  dollars  from 

these  mollusks  collected  from  the  oyster  beds  along  the  Atlantic  Coast. 
A  certain  kind  of  mollusk,  known  as  the  pearl  oyster,  secretes  within 
its  shell  the  pearls  of  commerce.  These  are  formed  of  a  material 
similar  to  that  found  on  the  inner  layers  of  the  fresh  water  mussel. 

E.   Reptiles 

140.  The  turtle.  —  The  body  of  a  turtle  may  be  divided  into  four 
regions;  namely,  head,  neck,  trunk,  and  tail.  The  larger  part  of  a 
turtle,  the  trunk,  is  covered  by  a  shell,  and  to  this  shell  the  bony 
skeleton  is  firmly  united.  The  two  pairs  of  legs,  however,  are  freely 
movable,  but  can  be  drawn  within  the  shell  for  protection.  The 
toes  of  the  feet  are  armed  with  sharp,  curved  nails,  and  the  legs  are 
covered  with  scales.  The  legs  are  used  for  walking  and  also  for 
swimming.  In  some  turtles  the  legs  become  broad  and  flat  and 
are  of  but  little  use  except  for  swimming. 

The  head,  neck,  and  tail  can  also  be  drawn  into  the  shell.  Scales 
cover  the  neck  and  part  of  the  head.  The  jaws  of  the  turtle,  often 
called  the  beak,  possess  no  teeth.  The  eyes,  protected  by  the  eye- 
lids, the  nostrils,  and  the  ear  openings,  are  readily  seen. 

Turtles  reproduce  by  means  of  eggs,  which  are  comparatively 
large.  Turtle  eggs  are  often  used  for  food.  These  animals  breathe 
throughout  their  entire  life  by  means  of  lungs. 


186 


ANIMAL  BIOLOGY 


141.    Suggestions  for  the  study  of  the  turtle.  —  Turtles  are  easily 
kept  at  home  or  in  the  laboratory.     The  pupil  should  verify  the 


FIG.  134.  —  Lizard  of  the  Southwest   (commonly  known   as  the  "horned 

1     toad"). 

statements  given  above  concerning  the  turtle,  and  should  then  write 
an  account  of  his  observations  in  his  notebook ;  or  a  well-labeled 
drawing  will  cover  most  of  the  ground.  The  pupil  should  also  ob- 
serve and  describe  in  his  notebook  the  methods  by  which  the  turtle 

feeds,  crawls,  swims,  and 
protects  its  head,  legs,  and 
tail. 


142.  Relatives  of  the 
turtle.  —  Animals  related 
to  the  turtle  are  the  lizards 
(Fig.  134),  alligators  and 
crocodiles,  and  snakes  (Fig. 
135),  all  of  these  animals 
being  known  as  reptiles. 
None  of  the  reptiles,  other 
than  the  turtles,  possess  a 
shell,  but  all  are  covered 
with  scales,  and  have  toes 
armed  with  claws,  except 


FIG.  135.— The  rattlesnake. 


ADDITIONAL  ANIMAL   STUDIES  187 

the  snakes  which  have  no  appendages.  Unlike  the  turtles  the  jaws  of 
all  other  reptiles  contain  sharp  teeth,  used  in  holding  their  prey,  and 
in  the  rattlesnake  and  copperhead  some  of  these  teeth  are  provided 
with  poison  glands.  None  of  the  other  reptiles  in  the  northern  part 
of  the  United  States  are  in  any  way  dangerous  to  man.  Indeed, 
many  snakes  destroy  large  numbers  of  rats  and  mice,  while  lizards 
catch  large  numbers  of  insects.  The  hide  of  the  alligator  is  of 
considerable  value  for  leather.  All  reptiles  breathe  throughout 
their  life  by  lungs,  and  most  of  them  reproduce  by  eggs,  which 
are  hatched  by  the  warmth  of  the  sun. 

F.   Mammals 

143.  Characteristics  of  mammals.  —  In  this  class  of  vertebrates 
are  included  domesticated  animals  such  as  the  cow,  sheep,  horse, 
camel,  dog,  and  cat.  Let  us  consider  the  structure  of  some  of  these 


FIG.  136.  —The  sperm  whale. 


animals  to  see  why  they  should  be  grouped  together.  We  are 
familiar  enough  with  the  animals  named  above  to  know  that  they  all 
have  a  head,  neck,  trunk,  and  tail  and  that  these  regions  are  covered 
with  hair.  A  few  mammals,  e.g.  the  baboons,  have  no  tail,  and  a 
few  are  nearly  destitute  of  hair,  like  the  whales  (Fig.  136) ;  but  all  of 
them  nourish  their  young  on  milk  produced  in  certain  organs 
known  as  mammary  glands;  hence  these  animals  are  called 
mammals. 

The  organs  of  the  head,  namely  the  ears,  eyes  with  eyelids,  and  the 
nostrils,  are  prominent  in  all  common  mammals,  but  vary  in  size  and 
shape.  The  jaws  have  teeth  set  in  sockets,  but  the  number  and 
kinds  of  teeth  vary  greatly.  Rats,  rabbits,  and  squirrels,  for 


188 


ANIMAL  BIOLOGY 


example,  have  sharp  cutting  teeth  (incisors)  and  grinding  teeth 
(molars).  Others,  e.g.  dogs,  cats,  lions,  and  tigers,  have  sharp  pointed 
incisors  and  molars  and  in  addition  long  canine  teeth  for  tearing 
their  food.  In  horses,  cows,  and  other  herbivorous  animals  the 
grinding  teeth  are  especially  developed,  while  canine  teeth  are  either 
wanting  or  are  relatively  small. 

All  these  animals  have  four  legs,  but  the  relative  size  of  the  front 
and  hind  legs  may  differ  greatly.     In  a  kangaroo,  for  instance,  the 


JUetouArpal  Bones  "' 


FIG.  137.  —  Skeleton  of  the  horse. 


hind  legs  are  very  large,  while  the  front  pair  are  so  small  as  to  be 
practically  useless.  Then,  too,  the  nails  on  the  toes  vary  con- 
siderably. The  fingers  and  toes  of  man  are  protected  on  a  surface 
by  nails.  A  horse  has  only  one  toe  on  each  foot,  and  the  nail  for 
that  toe  is  developed  into  a  hoof.  Cows  and  sheep  have  two  toes 
on  each  foot  similarly  protected.  On  this  account  these  mammals 
and  others  like  them  are  called  the  hoofed  mammals. 


ADDITIONAL  ANIMAL   STUDIES  189 

An  examination  of  the  skeleton  of  a  horse  (Fig.  137)  or  of  most 
mammals,  shows  that  the  skeleton  consists  of  bones  similar  to  those 
of  man.  Thus,  for  instance,  there  is  the  spinal  column  made  up  of  a 
series  of  more  or  less  similar  bones,  with  a  skull  that  may  vary  a 
great  deal  in  shape  from  that  of  man,  but  still  may  consist  of  similar 
bones.  The  shoulder  bones  and  hip  bones  can  be  readily  distin- 
guished. The  bones  of  the  legs  are  for  the  most  part  much  alike, 
but  in  the  foot  there  is  frequently  a  wide  variation,  as  in  the  case  of 
the  one-toed  foot  of  the  horse,  the  two-toed  foot  of  a  cow,  the  three 
toes  of  the  tapir,  the  four  of  a  hippopotamus,  and  the  five  of  the 
dog  or  of  man. 

144.  Suggestions  for  the  study  of  a  mammal.  —  Follow  the  gen- 
eral account  given  above  and  describe  the  corresponding  structures 
of  a  horse,  dog,  cat,  or  other  mammal.     Thus,  for  instance,  name 
the  regions  present,  and  describe  the  character  of  the  covering  of 
each  region.    Then  describe  the  situation  and  parts  of  the  eyes,  the 
situation,  size,  and  shape  of  the  external  ears,  the  location  of  the 
nostrils,  and  so  on  to  the  end  of  the  study.     Lastly,  describe  the 
methods  of  locomotion  of  the  animal,  and  its  food  and  feeding 
habits. 

145.  Economic  importance   of  mammals.  —  The  mammals  in- 
clude many  of  our  most  useful  animals  as  well  as  those  that  are  very 
dangerous.    Our  common  beasts  of  burden,  horses  and  mules  in  this 
country,  the  llama  of  South  America,  the  elephant  and  camel  of 
Asia  and  Africa,  are  all  mammals.     This  group  of  animals  also  fur- 
nishes us  with  an  immense  amount  of  material  valuable  for  food  or 
clothing  (e.g.  the  cow,  deer,  sheep,  pig,  seal).     The  group  of  car- 
nivorous mammals  contains  one  of  man's  most  devoted  friends  and 
protectors,  the  dog.     To  the  same  order  as  the  dog,  however,  belong 
the  wolves,  lions,  tigers,  hyenas,  and  wild  cats;    all  these  have 
canine  teeth  which  they  use  with  deadly  effect  in  tearing  their  prey. 
The  gnawing  mammals  (e.g.  rats  and  mice)  besides  being  a  nuisance, 
do  a  great  deal  of  damage.     The  rat  also  scatters  diseases  like 
cholera  and  bubonic  plague.    Some  rodents,  the  beaver,  for  example, 


190  ANIMAL  BIOLOGY 

are  valuable  on  account  of  their  fur.  The  rapacity  of  man,  however, 
has  nearly  exterminated  these  very  interesting  animals. 

G.  Classification  of  Animals 

146.  Vertebrates  and  invertebrates.  —  All  animals  may  be  divided 
into  two  great  groups,  known  respectively  as  vertebrates  and  inverte- 
brates.    To 'the  first  group  belong  the  animals  that  have  a  "  back- 
bone "  or  spinal  column  composed  of  a  series  of  bones  known  as 
vertebrae.     To  this  group  belong  fishes,  frogs,  turtles,  birds,  rabbits, 
and  human  beings,  for  all  of  them  have  a  spinal  column  made  up  of 
vertebrae.     Insects,  earthworms,  and  oysters,  on  the  other  hand, 
have  no  backbone ;  hence,  they  are  called  invertebrates  (i.e.  ani- 
mals without  vertebrae). 

147.  Summary  of  the  classification  of  the  invertebrates.  —  While 
the  vertebrates,  on  account  of  their  size,  are  more  familiar  to  most 
people,  in  reality  there  are  a  great  many  more  kinds  of  inverte- 
brates  than   vertebrates.     For   example,    over   300,000   different 
species  of  insects  have  been  described,  more  than  all  other  species 
of  animals  put  together.     The  invertebrates  are  divided  by  zoolo- 
gists into  ten  or  more  branches  or  subkingdoms,  some  of  the  most 
common  of  which  are  named  in  the  table  on  pages  192  and  193. 

148.  Summary  of  the  classification  of  the  vertebrates.  —  The 

vertebrate  branch  of  the  animal  kingdom  is  divided  into  five  distinct 
classes.  The  striking  characteristics  of  each  of  these  classes  will  be 
seen  by  studying  the  table  on  page  194. 

149.  Reproduction  among  the  vertebrates.  —  Among  the  ani- 
mals belonging  to  the  two  lowest  vertebrate  groups,  namely,  the  fish 
and  amphibia,  the  female  forms  eggs  within  the  body  and  deposits 
them  in  the  water.     Before  these  eggs  can  develop,  however,  they 
must  be  fertilized  by  sperm-cells  produced  by  the  male,  and  this  is 
likewise  true  of  all  the  higher  animals  and  plants.     The  fertilized 
eggs  develop  into  embryos  by  the  process  of  cell  division,  and  enough 
food  is  stored  in  the  egg  to  supply  the  young  animal  until  it  can 
secure  its  own  food.     Much  the  same  is  true  also  in  the  case  of  rep- 


ADDITIONAL  ANIMAL   STUDIES  191 

tiles,  except  that  the  eggs  are  usually  laid  in  the  sand  and  left  to 
develop  by  the  warmth  of  the  sun.  There  are,  however,  certain 
exceptions  to  the  general  statements  made  above.  Some  of  the 
sharks,  for  example,  and  certain  of  the  snakes,  instead  of  depositing 
eggs  that  develop  into  embryos  in  the  water  or  on  land,  retain  the 
eggs,  and  the  young  are  born  in  a  form  much  like  that  of  the  adult. 

Very  few  of  the  animals  belonging  to  the  classes  that  we  have 
been  discussing  (namely,  the  fishes,  amphibia,  and  reptiles)  ever 
take  any  care  of  their  young.  The  great  majority  of  birds,  however, 
not  only  build  nests  in  which  to  lay  their  eggs,  but  they  also  brood 
over  their  eggs  until  they  are  hatched,  and  then  the  parents  feed 
the  young  until  they  are  ready  to  fly. 

A  few  of  the  lowest  mammals,  like  most  of  the  vertebrates  named 
above,  lay  eggs.  By  all  the  common  mammals,  however,  the  eggs 
are  not  laid,  but  as  was  the  case  with  certain  sharks  and  snakes,  the 
eggs  develop  into  a  form  resembling  the  parent,  before  being  born. 
All  mammals  at  birth,  unlike  birds,  are  unable  to  eat  the  food  that 
is  used  by  their  parents.  Hence,  a  form  of  food  that  is  easily  digest- 
ible must  be  furnished.  This  is  secreted  by  certain  cells  of  the 
adults  in  the  form  of  milk.  The  masses  of  cells  that  secrete  milk 
are  known  as  mammary  glands,  and  because  of  the  presence  of  these 
glands  in  all  animals  of  this  the  highest  group  of  vertebrates,  this 
class  is  known  as  the  mammals. 


192 


ANIMAL  BIOLOGY 


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194 


ANIMAL  BIOLOGY 


CLASS 

EXAMPLE 

COVERING 
OF  BODT 

WARM  OR 
COLD 
BLOODED  1 

APPENDAGES  USED 
IN  LOCOMOTION 

ORGANS  OP 
RESPIRATION 

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Codfish 

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Naked 

Cold 

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Reptiles 

Turtles 

Scaly 

Cold 

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Lizards 

skin 

blooded 

pend.     Toes 

out  life 

with  claws 

Birds 

Robins 

Skin 

Warm 

Anterior     ap- 

Lungs 

Sparrows 

with 

blooded 

pend,  wings; 

feathers 

poster,      ap- 

pend,     with 

claws 

Mam- 

Cows 

Skin 

Warm 

Paired  append. 

Lungs 

mals 

Man 

with 

blooded 

with  nails 

hair 

1  Cold-blooded  animals  are  those  animals  in  which  the  tempera- 
ture of  the  blood  changes  with  the  temperature  of  their  surround- 
ings. Warm-blooded  animals,  on  the  other  hand,  maintain  under 
normal  conditions  an  almost  constant  temperature.  The  tempera- 
ture of  the  human  body,  for  example,  is  98.6°  F.,  which  is  usually 
higher  than  the  temperature  of  the  earth,  air,  and  water;  con- 
sequently when  we  touch  a  fish  or  frog,  the  animal  feels  cold. 


LOUIS  PASTEUR 

CHEMIST  AND   BIOLOGIST 

"  He  saved  more  lives  than  Napoleon  took  in  all  his  wars." 

See  pages  168-170. 


HUMAN  BIOLOGY 

CHAPTER  I 
THE   GENERAL   STRUCTURE   OF   THE   HUMAN   BODY 

1.  Regions  of    the  body.  —  In  man  and  in  most  other 
mammals  one  can  distinguish  at  least  three  regions ;  namely, 
the  head,  neck,  and  trunk.     To  the  trunk  are  attached  two 
pairs  of  appendages ;  namely,  two  arms  and  two  legs,  or,  as 
they  are  more  often  called  in  the  descriptions  of  the  lower 
animals,  the  four  legs.     If  the  front  wall  of  the  trunk  (com- 
posed largely  of  skin  and  muscle)  were  removed,  it  would  be 
found  that  this  region  of  the  human  body  is  divided   into 
an  upper  story  or  chest  cavity  (Fig.  1),  and  a  lower  story  or 
abdominal  cavity »    These  two  cavities,  are.  separated  from 
each   other  by  a  flexible   partition   called  the   diaphragm, 
which  is  composed  largely  of  muscle  more  or  less  in  the  form 
of  a  dome.     The  chest  and  abdominal  cavities,  separated  by 
a  diaphragm,  are  characteristic  of  all  mammals. 

2.  Organs  of  the  body.1  —  When  we  study  the  body  more 
closely,  especially  its  interior,  we  find,  in  various  regions, 
parts  that  carry  on  special  kinds  of  work  (Fig.  2).     Within 
the  chest  cavity  is  the  heart,  which  forces  blood  through  the 

1  Each  of  the  structures  named  in  this  paragraph  should  be  demon- 
strated on  a  manikin  or  a  chart  before  the  textbook  lesson  is  as- 
signed. While  studying  the  lesion,  the  pupil  should  find  in  Fig.  2 
each  of  the  organs  named. 

B  1 


HUMAN  BIOLOGY 


body.  Here,  also,  are  the  lungs,  which  take  in  oxygen  and 
give  it  to  the  blood,  and  which  remove  carbon  dioxid,  water, 
and  other  waste  matters  from  the  blood.  Below  the  dia- 
phragm are  the  stomach  and  the  intestines,  the  liver  and  the 


spinal  cord 
(composed  of 
nerve  cells 
and  nerve 
fibers) 


spinal  column 
(composed  of 
vertebrae  and 
cartilage) 


chest  cavity 


diaphragm 


abdominal  cavity 


FIG.  1.  —  Longitudinal  section  of  trunk  (side  view). 

pancreas,  all  of  which  help  to  change  our  food  into  liquid 
form  ready  to  be  used  by  the  body.  All  these  and  other 
parts  of  the  body  are  called  organs.  An  organ  is  a  part  of  a 
living  body  that  has  some,  special  work  to  do;  this  special  work 
is  called  its  function.  Our  hands,  for  example,  are  organs 


THE  GENERAL   STRUCTURE  OF  THE  HUMAN  BODY    3 


because  with  them  we  do  some  special  work  like  writing, 
sewing,  or  playing  the  piano. 

3.    Tissues  of  the  body.  —  When  we  squeeze  the  arm  or 
the  hand,  we  feel  the  hard  bones  within  that  form  the  skele- 


right  lung  — 


liver  — 


—  diaphragm 


large  intestine 
opened 


~~  large  intestine 


small  intestine 
(opened) 


bladder 


FIG.  2.  —  Organs  of  chest  and  abdomen  (front  view). 

ton.  We  can  raise  from  the  bones  the  softer  fleshy  material, 
which  is  composed  of  muscle  covered  by  skin.  By  clenching 
the  fingers  tightly  we  can  see  and  feel  on  the  inner  side  of 
the  wrist  the  tough  cords  or  tendons  of  connective  tissue  that 


4  HUMAN  BIOLOGY 

attach  the  muscles  to  the  bones.  If  we  run  a  clean  needle 
point  into  the  finger,  blood  flows ;  in  this  way  we  discover 
another  of  the  materials  found  in  our  hand ;  namely,  blood. 
This  experiment  also  demonstrates  that  the  human  body  has 
some  structures  by  the  help  of  which  sensations  of  touch  or 
pain  are  perceived.  All  the  parts  of  the  hand  we  have  been 
enumerating  are  known  as  tissues.  For  the  present  a  tissue 
may  be  defined  as  one  of  the  building  materials  of  which  an 
organ  is  composed.  In  the  hand  we  have  found  evidence  of 
the  presence  of  bone  tissue,  muscle  tissue,  connective  tissue, 
blood  tissue,  and  nerve  tissue.  Other  kinds  of  tissue  will  be 
discussed  in  the  pages  that  follow. 

In  order  to  go  farther  in  our  study  of  structure  we  need 
the  aid  of  the  compound  microscope.  With  this  instrument 
we  discover  that  the  tissues  are  by  no  means  the  simplest 
part  of  an  animal. 

4.    Cells  lining  the  mouth.  —  Laboratory  study. 

Materials :  Cells  from  the  human  body  may  be  readily  prepared 
by  gently  scraping  with  the  finger  nail  the  mucous  membrane 
lining  the  mouth  and  then  rubbing  the  material  thus  obtained  on  a 
clean  glass  slide,  adding  a  drop  of  water  and  a  cover  glass.  The 
cells  may  be  stained  with  iodine  in  order  to  show  the  nucleus  more 
sharply.  If  time  allows,  prepared  sections  of  the  brain,  intestines, 
skin,  and  other  organs  of  the  body  may  well  be  shown. 

Examine  with  the  low  power  of  the  compound  microscope 
the  cells  prepared  as  described  above. 

1.  Describe  the  form  and  color  of  each  cell  before  it  is 

stained  with  iodine. 

2.  In  the  cells  stained  with  iodine  notice  a  body,  usually  near 

the  center,  that  is  more  deeply  stained  than  the  rest 
of  the  cell.  This  is  the  cell  nucleus,  and  the  rest  of 
the  cell  is  known  as  the  cell  body.  The  nucleus  may 
be  seen  in  the  unstained  cells  as  a  denser  portion. 


THE  GENERAL   STRUCTURE  OF  THE  HUMAN  BODY    5 


a.  Name,  now,  two  parts  of  a  cell  from  the  membrane 

lining  the  mouth. 

b.  State  the  form  and  position  of  the  cell  nucleus. 

3.  Make  a  drawing  of  two  of  the  cells  described  above  (each 

cell  to  be  represented  about  an  inch  in  diameter). 
Label  cell  body  and  cell  nucleus. 

4.  (Optional.)     Demonstrate  by  the  use  of  prepared  slides,  pic- 

tures, or  charts  that  the  brain,  the  intestine,  and  other  organs 
of  the  body  are  composed  of  cells  (Fig.  3). 

5.  Cells  and  protoplasm.1  —  Under  the  microscope  cells  at 
first  appear  to  be  only  plane  surfaces  surrounded  by  lines 
(Fig.  3).  In  reality, 
however,  each  cell 
has  not  only  length 
and  breadth,  but 
also  thickness. 
Cells  in  animals 
and  human  beings 
differ  from  those  in 
plants  in  never  hav- 
ing cell  walls  of  cel- 
lulose, and  often  cell 
walls  are  entirely 
wanting.  If  pres- 
ent, the  cell  wall  is  so  transparent  that  it  is  possible  to  look 
through  it  and  see  the  cell  body  and  nucleus  within. 

The  discovery  of  these  minute  bodies  of  which  organs  are 
composed  was  not  made  until  about  the  middle  of  the  last 
century  (1848).  With  the  rather  imperfect  microscopes 
then  in  use  the  two  discoverers,'  Schleiden  and  Schwann, 
could  see  the  walls  only,  and  they  did  not  know,  as  we  now 

1  Because  of  the  importance  of  emphasizing  cellular  structure, 
the  substance  of  §§  42  and  43,  "Plant  Biology,"  are  here  inserted. 


FIG.  3.  —  Cells  from  tissues  of  body. 


6 


HUMAN  BIOLOGY 


know,  that  the  most  important  part  of  the  cell  is  not  the 
lifeless  wall  of  cellulose,  but  the  living  substance  which  is 
found  inside  the  cell  wall,  making  up  a  large  part  of  the  cell 
body  and  cell  nucleus.  To  this  substance  is  given  the  name 
protoplasm.  We  know  now  that  the  living  substance  or  pro- 
toplasm is  the  essential  part,  while  the  wall  may  be  missing, 
so  that  in  such  a  case  there  is  no  resemblance  to  a  cell  or 
box.  Biologists  now  understand  a  cell  to  be  a  bit  of  proto- 
plasm (cell  body)  containing  a  nucleus  (which  is  a  denser  por- 
tion of  the  protoplasm). 

Protoplasm,  when  examined  with  the  highest  powers  of 
the  microscope,  appears  as  a  colorless,  semifluid  substance, 
in  which  are  often  seen  solid  particles  or  granules,  which  are 
probably  little  masses  of  food.  The  nucleus,  as  already 
stated,  is  commonly  found  near  the  center  of  the  cell,  and  is 
composed  of  protoplasm  denser  than  the  protoplasm  of  the 
rest  of  the  body  of  the  cell.  -The  appearance  and  composition 
of  the  protoplasm  surrounding  the  nucleus,  that  is,  the  cell 
body,  may  be  well  represented  by  raw  white  of  egg ;  but  in 
making  this  comparison  one  should  bear  in  mind  that  the 
white  of  an  egg  is  not  living  substance. 

6.  Assimilation,  growth,  and  cell  division.  —  Within  the  pro- 
toplasm are  foods  in  solution  (such  as  sugar  protein,  and 
mineral  matters).  These  are  used  by  cells  in  their  growth 
and  repair,  and  in  the  various  kinds  of  work  that  they  carry 
on.  In  the  human  body,  as  in  plants,  the  food  materials 
are  gradually  changed  by  protoplasm  into  living  substance 
like  itself.  To  this  process  is  given  the  name  assimilation 
(Latin,  ad  =  to  +  similis  '=  like) .  As  a  result  of  the  process 
of  assimilation  the  amount  of  protoplasm  of  course  increases 
and  the  cell  grows.  Were  this  process  to  continue  indefi- 
nitely, cells  would  come  to  be  large  in  size.  This,  however, 


THE  GENERAL   STRUCTURE  OF  THE  HUMAN  BODY     1 


does  not  occur ;  for  when  a  cell  reaches  its  normal  size,  the 
nucleus  divides  (Fig.  4),  and  the  halves  separate  from  each 
other  to  form  two  nuclei.  The  cell  body  now  divides  into 
two  parts,  and  cell  walls  are  formed  between  the  two  cells. 
Thus  are  produced  two  cells,  each  having  its  own  nucleus, 
and  these  in 
turn  assimilate 
and  divide.  In 
this  way  the 
number  of  cells 
increases  with 
the  growth  of 
the  body. 

7.  Cells  of  the 

blood.  If      We       A,  cell  before  divi-      B,  cell  with  divided  C,  single  cell  divided 

sion.  nucleus.  into  two  cells. 

were  to  examine 

With    the    Com-  FIG.  4.  —  CeU  division. 

pound  micro- 
scope a  drop  of  fresh  blood,1  we  should  find  that  it  is  not  the 
simple  red  liquid  it  seems  to  be ;  it  consists  of  solid  particles, 
called  blood  corpuscles,  floating  in  a  watery  liquid  known  as 
6/oot?  plasma.  These  corpuscles  are  single  cells.  Two  kinds 
can  be  distinguished,  which  from  their  color  are  known  as 
red  corpuscles  and  white  corpuscles  (Fig.  5). 

There  are  three  hundred  to  seven  hundred  times  as  many 
red  corpuscles  as  white.  We  shall  first  consider  the  white 
corpuscles.  Each  consists  of  a  minute  bit  of  protoplasm 
in  which  is  imbedded  a  nucleus.  These  cells  of  the  blood 

1  The  blood  may  be  easily  obtained  by  tying  a  cord  tightly  about 
the  finger  and  then  pricking  it  with  a  needle  cleaned  by  an  antiseptic 
like  peroxid  of  hydrogen  or  by  heating  it  in  a  flame.  A  drop  of 
blood  is  squeezed  out  upon  a  glass  slide  and  covered  with  a  thin 
cover  glass. 


8 


HUMAN  BIOLOGY 


have  a  characteristic  method  of  locomotion,  in  the  process 
of  which  they  change  their  shape ;  they  can  creep  along  in 
a  direction  opposite  to  that  of  the  blood  current,  and  they 


red  corpuscles 
surface  view 


red  corpuscles 
edge  view 


white  corpuscles 
nucleus  not  seen 


white  corpuscles 
nucleus  at  centre 
of  each 


FIG.  5.  —  Cells  of  human  blood. 

have  even  been  seen  forcing  their  way  through  the  walls  of 

small  blood  vessels  by  pushing  out  slender  processes  called 

false  feet.  They  then  wander  about  in  the  tissues  of  the 
body,  and,  as  we  shall  soon  see,  do  us  great 
service.  The  white  corpuscles  closely  re- 
semble in  structure  and  functions  a  kind 
of  single-celled  animal  called  the  Amoeba 
(A.B./Fig.  126). 

The  red  corpuscles  have  no  power  of  in- 
dependent   motion.     They    are    circular 

FIG.  6.  — Number  of  disks,  concave  on  both  surfaces.  Some 
idea  of  the  minute  size  of  these  cells  may 
be  gained  from  the  fact  that  ten  millions 

of  them  would  just  about  cover  a  space  one  inch  square. 

There  is  no  nucleus  in  the  red  corpuscles ;  they  are,  however, 

formed  from  cells  having  a  nucleus. 

1  A.  B.  =  "  Animal  Biology." 


10,000,000  red 
corpuscles  could 
be  enclosed  in  a 
single  layer  with- 
in this  square 
inch 


THE  GENERAL   STRUCTURE  OF  THE  HUMAN  BODY     9 

8.  Cells  in  other  tissues.  —  It  has  been  demonstrated  that 
nerve  tissue,  muscle  tissue,  and  other  building  materials  of 
the  body  are  all  composed  6f  cells  (Fig.  3).  A  tissue  may 
now  be  defined  as  a  building  material  of  the  body,  composed 
of  cells  of  the  same  kind. 


CHAPTER  II 

MICROORGANISMS  AND  THEIR  RELATION  TO  HUMAN 
WELFARE 

I.  STRUCTURE  AND  FUNCTIONS  OF  BACTERIA 

9.  Bacteria:1  their  microscopical  appearance  and  size. — 
In  the  preceding  chapter  we  considered  to  some  extent  the 
organs,  tissues,  and  cells  of  the  human  body.  However, 
before  we  discuss  further  the  structure  and  functions  of 
these  various  parts  of  our  bodies,  we  shall  study  in  some 
detail  certain  microscopic  plants  which  have  a  most  intimate 
relation  to  human  welfare.  Chief  among  these  are  the  tiny 
organisms  known  as  bacteria. 

Every  one  is  familiar  with  the  fact  that  if  a  bouquet 
of  flowers  is  left  for  some  time  in  a  vase  of  water,  the  stems 
decay  and  disagreeable  odors  are  given  off.  This  is  a  com- 
mon example  of  the  action  of  bacteria,  for  all  decay  is  due 
to  the  work  of  these  organisms.  When  we  come  to  examine 
the  flower  stems  or  the  putrid  water,  we  find  a  slimy  scum. 
If  we  put  a  drop  of  this  scum  on  a  slide,  cover  with  a  cover 
glass,  and  examine  with  the  highest  powers  of  the  microscope, 
we  usually  see  many  different  forms  of  living  things.  Some 
of  them  appear  relatively  large,  and  these,  as  we  have  already 
seen  (A.  B.,  Chapter  VI),  are  single-celled  animals.  A  closer 
examination  will  disclose  countless  numbers  of  very  minute, 

1  The  substance  of  this  section,  and  several  of  those  that  follow, 
appear  in  Part  I,  "Plant  Biology."  Many  teachers,  however,  find 
it  impracticable  to  discuss  bacteria  until  the  work  in  human  biol- 
ogy is  taken  up  ;  hence  the  repetition  of  this  material  in  this  volume. 

10 


MICROORGANISMS  AND  HUMAN   WELFARE 


11 


colorless  organisms ;  these  are  the  bacteria.  A  careful  study 
of  many  kinds  of  bacteria  shows  that  they  have  several  char- 
acteristic shapes  (see  Fig.  7),  by  means  of  which  they  may  be 
roughly  classified.  Some  are  rod-shaped  (like  a  firecracker), 
some  are  spheri- 
cal, or  egg-shaped, 
and  still  others  are 
spiral-shaped. 
Each  bacterium  is 
a  tiny  bit  of  trans- 
lucent protoplasm, 
inclosed  in  a  cell 
wall  of  cellulose. 
Thus  far  no  nu- 
cleus has  been  dis- 
covered  in  any 
kind  of  bacteria. 
Because  of  their 
cellulose  walls, 
and  because  of 
their  likeness  to  ~ 

certain  low  forms  n  0  (1  H 

of  green  plants,  bi-  H  rl  H  H 

U  UUU 

bacteria  bacteria  with 

reproducing  spores 

FIG.  7.  — Various  forms  of  bacteria. 


spherical  bacteria 
(cocoi) 


rod-shaped 
bacteria 
(bacilli) 


spiral  bacteria  (spirilla) 


ologists  now  regard 
these  organisms 
as  plants  rather 
than  animals.  ' 

Some  kinds  of  bacteria  have  one  or  more  long,  hairlike 
projections  from  the  ends,  called  cil'i-a,  which  give  the  germs 
still  further  resemblance  to  firecrackers.  These  cilia  lash 
about  rapidly,  and  thus  drive  the  cell  through  the  water. 
The  spiral  bacteria  roll  over  and  over,  and  advance  in  a  spiral 
path  like  a  corkscrew. 


12  HUMAN  BIOLOGY 

It  is  very  difficult  to  get  any  clear  notion  of  the  extreme 
minuteness  of  bacteria.  It  means  little  to  say  that  the 
rod-shaped  forms  are  -yrnnr  °f  an  mcn  m  length.  The  im- 
agination may  be  somewhat  assisted  if  we  remember  that 
fifteen  hundred  of  them  arranged  in  a  procession  end  to  end 
would  scarcely  equal  the  diameter  of  a  pin  head. 

10.  Microscopic  study  of  bacteria.  —  Laboratory  demon- 
stration. 

Place  on  a  glass  slide  a  drop  of  the  scum  found  on  the 
surface  of  a  hay  infusion,  and  cover  with  a  cover  glass. 
Examine  with  the  highest  powers  of  the  compound  microscope. 

1.  Describe  the  source  of  the  material  you  are  examining. 

2.  What  is  the  apparent  color  of  the  tiny  bodies  (bacteria) 

that  you  see  ? 

3.  Which  of  the  different  forms  of  bacteria  shown  in  Fig.  7 
•     do  you  find?     Draw  enlarged  figures  of  each  of  the 

shapes  that  you  find. 

4.  Do  any  of  the  bacteria  seem  to  be  in  motion?     If  so, 

describe  the  motion. 

11.  Reproduction    of    bacteria.  —  When    conditions    are 
favorable,  the  production  of  new  cells  goes  on  with  marvelous 
rapidity.     The   process  is  something   as  follows :    the  tiny 
cells  take  in  through  the  cell  wall  some  of  the  food  materials 
that  are  about  them,  change  this  food  into  protoplasm,  and 
thus  increase  somewhat  in  size.     The  limit  is  soon  reached, 
however,  and  the  bacterium  begins  to  divide  crosswise  into 
halves.     The   mother   cell  thus  forms   two'  daughter   cells 
by  making  a  cross  partition  (cell  wall  of  cellulose)  between 
the  two  parts  (Fig.  7) .     If  the  daughter  cells  cling  together, 
a  chain  or  a  mass  is  formed.      Oftentimes  they  separate 
entirely  from  each  other.     In  either  case  the  whole  mass  of 
bacteria  is  called  a  colony. 

It  usually  takes  about  an  hour  for  the  division  to  take 


MICROORGANISMS  AND  HUMAN    WELFARE  13 

place.  Suppose,  then,  we  start  at  ten  o'clock  some  morning 
with  a  single  healthy  bacterium.  If  conditions  are  favorable, 
there  would  be  two  cells  at  eleven  o'clock,  and  by  twelve 
o'clock  each  of  these  two  daughter  cells  would  form  two 
granddaughter  cells;  the  colony  would  then  number  four 
individuals.  Should  this  process  continue  for  twenty- 
four  hours  or  until  ten  o'clock  on  the  day  after  the  single 
bacterium  began  its  race,  the  colony  would  number  16,777,- 
216  bacteria.  "  It  has  been  calculated  by  an  eminent 
biologist,"  says  Dr.  Prudden,1  "  that  if  the  proper  conditions 
could  be  maintained,  a  rodlike  bacterium,  which  would 
measure  about  a  thousandth  of  an  inch  in  length,  multiply- 
ing in  this  way,  would  in  less  than  five  days  make  a  mass 
which  would  completely  fill  as  much  space  as  is  occupied 
by  all  the  oceans  on  the  earth's  surface,  supposing  them  to 
have  an  average  depth  of  one  mile." 

12.  Spore  formation  in  bacteria.  —  Such  startling  possi- 
bilities as  those  suggested  in  the  preceding  section  fortunately 
can  never  become  realities,  for  favorable  conditions  soon 
cease  to  exist  and  the  cells  either  die  or  cease  to  multiply. 
Sometimes,  when  food  or  moisture  begins  to  fail,  the  pro- 
toplasm within  each  cell  rolls  itself  into  a  ball  and  covers 
itself  with  a  much  thickened  wall.  This  protects  it  until 
it  again  meets  with  conditions  favorable  for  growth.  The 
process  we  have  been  describing  is  known  as  spore  formation  ; 
the  tiny  protoplasmic  sphere  is  called  a  spore,  and  its  dense 
covering  a  spore  wall  (Fig.  7).  In  this  condition  bacteria 
may  be  blown  hither  and  yon  as  a  part  of  the  dust.  They 
may  be  heated  even  above  the  temperature  of  boiling  water 
without  being  killed.  When  at  length  they  settle  down  on 


Story  of  the  Bacteria,"  by  Dr.  T.  Mitchell  Prudden. 
G.  P.  Putnam's  Sons,  New  York. 


14  HUMAN  BIOLOGY 

a  moist  surface  that  will  supply  them  with  food,  the  spores 
burst  their  thick  envelope,  assume  once  more  their  rod- 
shaped  or  spiral  form,  and  go  on  feeding,  assimilating,  and 
reproducing  their  kind. 

II.   OCCURRENCE  OF  BACTERIA 

13.  Are  bacteria  present  in  the  air.  —  Laboratory 
demonstration. 

Materials:  The  best  method  of  cultivating  bacteria  is  by  the 
use  of  a  nutrient  agar  mixture  in  Petri  dishes,  which  is  prepared  as 
follows :  — 

To  prepare  1000  cc.  (about  a  quart)  of  agar  mixture,  weigh  out 
10  grams  of  salt,  10  grams  of  peptone,  10  grams  Liebig's  beef  ex- 
tract, and  10  grams  of  agar.  Measure  into  an  agate  stewpan 
1000  cc.  of  water,  and  stir  in  the  salt,  peptone,  beef  extract,  and 
agar  (the  latter  having  been  cut  into  small  pieces).  Heat  the 
mixture  in  a  double  boiler  until  the  agar  is  wholly  melted.  Slowly 
stir  in  just  enough  baking  soda  to  cause  red  litmus  paper  to  turn 
blue ;  i.e.  the  mixture  should  be  slightly  alkaline.  When  the  pieces 
of  solid  agar  have  all  disappeared,  the  hot  liquid  should  be  filtered 
into  flasks  of  250  cc.  capacity  through  several  rather  thick  layers  of 
absorbent  cotton  placed  in  a  funnel.  This  filtration  might  well  be 
done  by  placing  the  flasks  in  a  steam  sterilizer.  If  the  filtrate  is 
not  clear,  the  liquid  should  be  poured  through  the  same  layers  of 
cotton  till  it  does  become  clear.  Care  should  be  taken  to  keep  the 
agar  mixture  hot  during  the  filtering  process,  otherwise  the  agar 
will  not  pass  through  the  cotton.  When  the  flasks  are  nearly  full, 
plug  the  mouth  of  each  with  a  large  wad  of  cotton  batting,  put 
them  into  a  steam  sterilizer,  and  heat  them  at  least  thirty  minutes 
on  each  of'  three  successive  days  to  make  sure  that  all  germs  and 
their  spores  are  killed.  The  flasks  of  agar  may  then  be  kept  as  a 
stock  mixture  until  needed. 

Carefully  clean  and  dry  enough  Petri  dishes  to  supply,  if  pos- 
sible, seventeen  or  more  dishes  for  experiments  with  each  division 


MICROORGANISMS  AND  HUMAN   WELFARE          15 

of  students.  Put  the  closed  dishes  in  an  oven  and  heat  to  a  high 
temperature  (150°  C.)  for  an  hour  to  kill  any  germs  or  spores  that 
may  be  on  the  dishes.  Allow  the  oven  to  cool  before  opening  the 
door ;  otherwise  the  dishes  are  likely  to  crack. 

To  fill  the  Petri  dishes,  melt  the  agar  mixture  in  a  steam  sterilizer, 
then  arrange  the  sterilized  Petri  dishes  along  the  edge  of  a  horizontal 
surface.  Carefully  remove  the  cotton  plug  from  the  flask,  lift  one 
edge  of  the  cover  of  one  of  the  Petri  dishes,  pour  enough  of  the  hot 
agar  mixture  into  the  lower  part  of  the  dish  to  make  a  layer  about  an 
eighth  of  an  inch  deep,  and  quickly  replace  the  cover  on  the  dish. 
Quickly  pour  into  each  of  the  dishes  in  turn.  After  the  agar  has 
hardened,  the  dishes  are  ready  for  the  experiments.  Any  agar 
mixture  left  in  the  flasks  should  be  sterilized  for  thirty  minutes  on 
each  of  three  successive  days  in  order  to  make  sure  that  it  will  keep 
for  subsequent  use. 

Treat  several  of  the  Petri  dishes  of  agar  as  follows :  Label 
the  first  dish  No.  1  and  keep  it  closed  throughout  the  experi- 
ments. Place  a  second  Petri  dish  on  the  desk  of  a  pupil, 
remove  the  cover  and  thus  for  ten  minutes  expose  the  surface 
of  the  agar  to  the  air  of  a  classroom  or  laboratory;  label 
it  dish  No.  2.  In  a  similar  manner  expose  the  surface  of 
dish  No.  3  for  ten  minutes  to  the  air  near  the  floor  of  a  corri- 
dor through  which  classes  are  passing.  Put  all  three  dishes 
aside  for  a  few  days  in  a  dark  place  where  the  temperature 
is  80°  to  90°  (e.g.  in  a  furnace  room),  and  then  examine 
each  dish. 

1.  State  the  difference  in  the  treatment  of  dishes  No.  1,  No.  2, 

and  No.  3.  In  what  respects  have  all  three  been 
treated  alike? 

2.  The  spots  on  the  surface  of  the  agar  are  colonies  of  bacteria, 

each  one  of  which  has  developed  from  a  single  bacterium 
(see  Fig.  11).  Which  of  the  three  dishes  has  the  largest 
number  of  bacteria  colonies? 

3 .  Suggest  a  reason  for  the  difference  in  the  number  of  bacteria 

colonies  in  the  three  dishes. 

4.  What  do  you  infer,  therefore,  as  to  the  presence  of  bacteria 

in  the  air? 


16  HUMAN  BIOLOGY 

5.  (Optional.)  Make  careful  drawings  at  intervals  of  several  days 
to  show  the  difference  in  the  number  of  colonies  in  the  dishes, 
and  the  change  in  the  size  and  appearance  of  the  colonies. 

14.  Are  bacteria  present  in  water,  milk,  and  other  foods  ? 
—  Laboratory  demonstration. 

Allow  the  water  to  run  from  the  faucet  for  several  minutes, 
and  then  spread  a  drop  on  the  surface  of  dish  No.  4.  Spread 
a  drop  of  milk  on  the  surface  of  the  agar  in  dish  No.  5.  On 
the  agar  surface  of  dish  No.  6  put  a  bit  of  raw  meat,  a  bit 
of  apple  peel,  and  bits  of  other  kinds  of  food.  Put  the  dishes 
in  a  warm,  dark  place  as  directed  above,  and  examine  at  the 
end  of  several  days. 

1.  State  the  difference  in  the  treatment  of  dishes  No.  4,  No.  5, 

and  No.  6. 

2.  In  which  of  the  three  dishes  do  you  find  bacteria  colonies  ? 

Describe  the  colonies  in  each  dish  as  to  position,  number, 
and  color. 

3.  What  do  yon  infer  as  to  the  presence  of  bacteria  in  water, 

milk,  and  other  foods  that  you  have  tested? 

15.  Are  bacteria  present  on  various   parts  of  the  human 
body  ?  —  Laboratory  demonstration. 

Touch  the  surface  of  the  agar  in  dish  No.  7  with  the 
finger  tips ;  lay  a  hair  on  another  part  of  the  surface,  and 
touch  a  third  part  with  a  toothpick  that  has  been  used  to 
scrape  the  teeth.  Put  the  dish  in  a  warm,  dark  place  as 
above,  and  examine  at  the  end  of  several  days. 

Describe  fully  this  experiment,  stating  your  observations 
and  conclusions. 

16.  Distribution  of  bacteria. — From  our    study  of   the 
culture  dishes  we  have  learned  that  bacteria  are  very  com- 
mon   organisms.     In    fact,    they    are    doubtless    the    most 
abundant  of  all  living  things;   for  they  are  found  not  only 
in  air,  water,  and  milk;    not  only  in  countless  numbers 
wherever  dead  plant  or  animal  material  is  allowed  to  accu- 
mulate ;  but  also,  unfortunately,  in  living  tissues. 


MICROORGANISMS  AND  HUMAN  WELFARE          17 

17.  To  determine  conditions  favorable  and  unfavorable 
for  the  growth  of  bacteria.  —  Laboratory  demonstration. 

A.  The  effect  of  different  degrees  of  temperature.  —  Expose 

for  ten  minutes  three  Petri  dishes  of  nutrient  agar 
to  the  air  in  a  room  or  corridor  when  classes  are 
moving  about.  Cover  the  dishes  and  label  them 
No.  8,  No.  9,  and  No.  10,  respectively.  Put  dish 
No.  8  in  a  temperature  of  80°  to  100°  F.,  and  dish 
No.  9  in  the  refrigerator,  or  in  some  other  equally 
cold  place.  Dish  No.  10  should  be  put  in  a  steam 
sterilizer  and  heated  for  thirty  minutes  on  each 
of  three  successive  days;  it  should  then  be  kept 
in  a  warm,  dark  place. 

1.  Describe  the  difference  in  the  treatment  of  dishes  8, 

9,  and  10. 

2.  At  the  end  of  a  week  examine  each  of  the  three  dishes. 

What  difference  do  you  find  in  the  relative  number 
of  colonies  in  them? 

3.  What  do  you  conclude,  therefore,  as  to  the  influence 

of  each  of  these  three  different  degrees  of  tempera- 
ture on  the  growth  of  bacteria? 

B.  Pasteurization  of  milk.  —  (Optional.)     If  possible  secure  a  Pas- 

teurizer1 (Fig.  8).  Carefully  clean  with  soap  and  hot 
water,  inside  and  out,  four  of  the  glass  bottles,  fill  each 
with  milk  that  is  fresh,  and  fasten  on  the  stoppers. 

1  Home  Pasteurizers, —  System  Nathan  Straus, — each  supplied 
with  bottles  and  stoppers,  may  be  bought  at  the  Nathan  Straus 
Pasteurized  Milk  Laboratory,  348  East  32d  St.,  New  York  City,  or 
at  any  of  the  Laboratory  depots  situated  throughout  the  city.  The 
manufacturer's  price  for  the  entire  outfit  is  $1.50.  The  authors  are 
indebted  to  the  Nathan  Straus  Laboratories  for  the  cut  of  the  Pas- 
teurizer, and  for  the  directions  quoted  above.  The  circular  also 
contains  the  following  statements.  "The  advantage  of  Pasteuriza- 
tion over  other  systems,  such  as  sterilization  or  boiling,  consists  in  the 
lower  degree  of  heat  applied,  which  is  sufficient  to  kill  all  noxious 
germs,  while  the  nourishing  quality  and  good  taste  of  the  milk  are 
retained.  .  .  .  Before  use,  warm  the  milk  —  in  the  bottles  —  to 
blood  heat.  Never  pour  it  into  another  vessel.  The  milk  must  not 
be  used  for  children  later  than  twenty-four  hours  after  Pasteuriza- 
tion. Never  use  remnants." 


18  HUMAN  BIOLOGY 

Keep  one  bottle  at  the  temperature  of  the  laboratory, 
labeling  it  bottle  No.  1,  and  put  another,  bottle  No.  2, 
in  the  refrigerator.  Pasteurize  the  other  two  bottles  in 
accordance  with  the  following  directions  :  — 
"Set  the  bottles  into  the  tray.  .  .  .  The  pot  is  then  placed  on 
a  wooden  surface  (table  or  floor)  and  filled  to  the  three 
supports  (in  the  pot)  with  boiling  water.  Place  the  tray 


FIG.  8.  —  Straus  Pasteurizer. 

with  the  filled  bottles  into  the  pot,  so  that  the  bottom  of 
the  tray  rests  on  the  three  supports,  and  put  cover  on 
quickly.  After  the  bottles  have  been  warmed  up  by  the 
steam  for  five  minutes,  remove  the  cover  quickly,  turn 
the  tray  so  that  it  drops  into  the  water.  The  cover  is 
to  be  put  on  again  immediately.  This  manipulation  is 
to  be  made  very  quickly,  so  that  as  little  steam  as  pos- 
sible can  escape.  Thus  it  remains  for  twenty-five 


MICROORGANISMS  AND  HUMAN   WELFARE          19 

minutes.  Now  take  the  tray  out  of  the  water,  cool  the 
bottles  with  cold  water  and  ice  as  quickly  as  possible, 
and  keep  them  at  this  low  temperature  till  used." 
Place  one  bottle  of  Pasteurized  milk  (No.  3)  beside  the  bottle 
in  the  room  temperature,  and  the  other  (No.  4)  in  the 
refrigerator  beside  bottle  No.  2. 

1.  At  the  end  of  three  days  shake  the  two  bottles  kept  at 

the  room  temperature  and  open  them.  Smell  or  taste 
of  the  milk  in  each.  State  your  observations  and  con- 
clusions. 

2.  In  a  similar  manner,  test  the  two  bottles  that  have  been 

kept  on  ice  for  a  week.  State  your  observations  and 
conclusions. 

3.  Why  are  milk,  meat,  and  other  foods  of  the  kind  put  into 

the  refrigerator,  especially  in  summer  time  ?  Does  this 
kill  the  bacteria  ?  How  do  you  know  ? 

4.  Why  are  meats  cooked,  milk  Pasteurized,  and  fruits  boiled 

before  they  can  be  kept  for  any  length  of  time  ? 

C.  The  effect  of  lack  of  moisture.  — Expose  for  ten  minutes 
two  Petri  dishes  of  nutrient  agar  in  a  dusty  room  or 
corridor  (as  in  A  above).  Place  the  two  dishes  (No. 
11  and  No.  12  side  by  side  in  a  warm  room  (over 
90°).  Cover  dish  No.  11  and  leave  dish  No.  12  un- 
covered. 

1.  Describe   the  similarity   and   the   difference   in   the 

treatment  of  dishes  11  and  12. 

2.  How  is  the  agar  mixture  affected  by   removing  the 

cover  ? 

3.  In  which  dish  do  colonies  of  bacteria  develop? 

4.  What  do  you  conclude,  therefore,  as  to  the  necessity 

of  moisture  for  the  growth  of  bacteria? 

5.  Why  is  hay  dried  before  it  is  put  into  the  barn? 

Name  some  foods  used  by  man  that  are  kept  for 
a  long  time  after  being  dried. 

6.  As  a  conclusion  from  these  experiments  (in  A,  B  and 

C)  state  what  conditions  you  have  found  favorable 
for  the  growth  of  bacteria. 


20  HUMAN  BIOLOGY 

7.   State  also  what  conditions  you  have  found  that  hin- 
der the  growth  of  bacteria. 

D.  The  effect  of  antiseptics.  —  Prepare  a  pure  culture  of 
bacteria  in  dish  No.  13  in  the  following  manner. 
Heat  a  dissecting  needle  on  a  piece  of  platinum  wire 
in  a  hot  flame  to  kill  all  the  germs  upon  it.  When 
it  cools,  touch  a  colony  of  bacteria  in  a  Petri  dish 
with  the  needle-point  or  wire ;  carefully  raise  the 
cover  of  dish  No.  13  and  make  several  scratches 
in  the  agar  (the  date  of  the  experiment  or  the  num- 
ber of  the  room  may  be  scratched  in  this  way). 
In  a  similar  way  prepare  dish  No.  14  and  then  pour 
over  the  surface  some  peroxid  of  hydrogen  or  other 
antiseptic  solution.  When  the  dishes  have  been 
treated  as  described  above,  put  them  in  a  warm, 
dark  place  for  several  days  ? 

1.  Describe  the  preparation  of  dishes  13  and  14. 

2.  In  which  of  the  two  dishes  do  you  find  no  colonies  of 

bacteria  at  the  end  of  several  days  ? 

3.  Peroxid  of  hydrogen  is  employed  in  treating  wounds. 

How  do  you  know  that  bacteria  are  killed  by  this 
treatment? 


III.  BACTERIA  AS  THE  FRIENDS  OF  MAN 

18.  Relation  of  bacteria  to  soil  fertility.  —  Having  dis- 
cussed somewhat  the  structure  and  functions  of  bacteria, 
we  are  now  to  consider  the  great  importance  of  these  mi- 
croscopic organisms  to  human  welfare.  In  the  first  place, 
were  it  not  for  their  never  ending  activity,  all  life  upon  the 
earth  would  soon  cease  to  exist.  Let  us  see  why  this  is  so. 
When  animals  or  plants  die,  their  bodies  fall  upon  the  ground, 
and  had  not  these  lifeless  masses  been  taken  care  of,  the 
whole  surface  of  the  earth  would  long  since  have  been  covered 
with  a  vast  number  of  unburied  organisms.  All  this  dead 
material,  however,  as  we  have  seen,  is  food  for  the  countless 


MICROORGANISMS  AND  HUMAN   WELFARE 


21 


bacteria;  they  cause  it  to  decay,  and  thus  decompose  it 
into  simpler  chemical  compounds  that  soak  into  the  earth  and 
may  then  be  used  in  the  nutrition  of  the  higher  plants.  And 
since  plants  are  constantly  taking 
from  the  soil  the  food  materials  that 
they  need,  this  soil  would  tend  to  be- 
come less  and  less  fertile  were  it  not 
for  the  work  of  the  bacteria  that  cause 
decomposition.  This  is  the  reason 
why  rotting  manure  adds  to  the  fer- 
tility of  soil. 

Again,  it  has  been  proved  that 
certain  kinds  of  bacteria  directly  in- 
crease the  amount  of  nitrogen  com- 
pounds that  are  so  essential  for  plant 
growth.  It  has  long  been  known  that 
corn  and  other  crops  will  grow  better 
in  soil  that  has  just  borne  a  crop  of 
peas,  beans,  clover,  or  other  members 
of  the  pea  family.  Within  recent 
years  an  explanation  of  this  fact  has 
been  found.  When  the  roots  of  these 
pod  bearing  plants  are  examined, 
small  swellings  are  seen  (Fig.  9). 
These  contain  multitudes  of  bacteria 
that  are  able  to  take  the  free  nitrogen 
from  the  air,  where  it  exists  in  such 
abundance,  and  store  it  away  in  the 
form  of  nitrates,  which  are  very  important  mineral  matters 
needed  by  all  crops.  Since  these  bacteria  can  be  put  into 
soils  that  do  not  have  them,  it  may  be  possible  in  the  near 
future  to  restore  much  of  the  fertility  that  has  been  lost 
(Fig.  10). 


FIG.  9.  —  Roots  of  horse 
bean,  with  tubercles. 


22  HUMAN  BIOLOGY 

19.  Relation  of  bacteria  to  the  flavors  of  food.  —  Again, 
many  of  the  flavors  of  food  are  due  to  the  action  of  bacteria. 
The  flesh  of  animals,  for  instance,  that  have  just  been  killed, 
is  often  tough  and  tasteless.  If  allowed  to  stand,  however, 
these  meats  become  tender  and  acquire  their  distinctive  fla- 
vors by  the  decomposing  action  of  bacteria.  A  similar  action 
takes  place  when  butter  or  cheese  ripens,  and  the  dairy  in- 
dustry has  been  perfected  to  such  a  degree  that  bacteria  of 

certain  kinds  have  been 
proved  to  give  rise  to  defi- 
nite flavors,  and  these 
bacteria  may  be  produced 
in  pure  cultures  for  the 
dairymen. 

20.  Bacteria  in  the  in- 
dustries. —  Without  the 
help  of  bacteria  the  prep- 
aration of  linen,  jute, 
and  hemp  would  be  im- 


FIG.  10. -Bacteria  from  root  tubercles.  .      All  these  Valu- 

able  products  are  plant 

fibers  which  are  connected  with  woody  materials  so  closely 
that  they  cannot  be  separated  without  first  subjecting 
the  stems  of  flax,  hemp,  and  jute  to  a  process  of  decay 
in  large  tanks  of  water.  Moisture  and  warmth  induce 
the  rapid  growth  of  germs,  and  the  resulting  decay  loosens 
the  tough  fibers  so  that  they  may  be  separated  from  the 
useless  parts  of  the  plant.  The  change  of  alcohol  into 
vinegar  is  also  caused  by  bacteria.  Formerly  in  the 
preparation  of  indigo  other  forms  of  bacteria  were  all- 
important,  but  at  the  present  time  indigo  is  largely  made 
artificially. 


MICROORGANISMS  AND  HUMAN   WELFARE         23 


IV.   BACTERIA  AS  THE  FOES  OF  MAN 

21.  Injurious  effects  of  bacteria.  —  Most  of  the  common 
bacteria  are  either  harmless  or  distinctly  beneficial  to  man- 
kind (18-20).     The  experiments  we  tried  with  milk  (17,8), 
however,  show  that  this  kind  of  food  soon  sours  unless  it  is 
kept  in  a  very  cold  place.     Every  housekeeper  knows  also 
that  meat  and  many  other  kinds  of  food  quickly  spoil  if 
they  are  not  cooked  or  otherwise  preserved.     In  a  following 
section  we  shall  consider  some  of  the  methods  that  are  used 
to  prevent  this  decaying  action  of  bacteria. 

Unfortunately,  too,  there  are  certain  germs l  that  find 
favorable  conditions  for  growth  in  living  animal  tissue,  and 
by  their  growth  cause  certain  diseases,  some  of  which  are 
tuberculosis,  diphtheria,  and  typhoid  fever.  In  later  sections 
we  shall  learn  that  these  disease-producing  bacteria  are  all 
too  common  in  dust,  water,  and  foods ;  but  we  shall  likewise 
see  that  scientists  are  fast  learning  effective  methods  of 
preventing  the  ravages  of  these  disease-producing  bacteria, 
which  are  called  by  Dr.  Prudden  "  Man's  Invisible  Foes."  2 

22.  Methods  of    food  preservation.  —  We  saw  in  (17,  A 
and  C)  that  bacteria  thrive  whenever  they  can  get  plenty  of 
food  and  moisture,  and  whenever  the  temperature  is  favor- 
able for  their  growth.     We  also  learned  that,  whenever  any 
one    of    these   necessary    conditions    is    wanting,   bacteria 
cease  to   carry  on  their  functions.     If,  then,  we  wish  to 

1  Disease-producing  bacteria  are  commonly  spoken  of  as  germs  or 
microbes. 

2  In  general  it  is  unwise  and  unnecessary  that  boys  and  girls 
should  be  taught  much  regarding  the  symptoms  and  effects  of  dis- 
ease ;  but  since  so  much  may  be  done  to  prevent  these  diseases  that 
we  have  mentioned  and  others  that  afflict  mankind,  it  is  essential 
that  the  young  should  learn  something  of  the  deadly  work  of  some 
of  the  germs  which  are  all  too  common. 


24  HUMAN  BIOLOGY 

keep  food  from  spoiling,  we  need  only  to  bring  about  con- 
ditions that  are  unfavorable  for  th^  growth  of  microor- 
ganisms. 

For  instance,  everybody  knows  that  meat,  milk,  and  eggs 
must  be  put  on  ice  in  summer  if  they  are  to  be  kept  for  any 
length  of  time.  Indeed,  many  food  materials  of  this  sort  will 
remain  in  a  more  or  less  fresh  condition  for  months  or  even 
years  if  they  are  in  cold  storage.  It  has  been  proved,  how- 
ever, that  food  products  kept  in  cold  storage  for  a  long  time 
are  often  unsafe  for  human  consumption.  On  the  other 
hand,  we  demonstrated  (17,  A)  that  a  high  degree  of  heat  will 
kill  bacteria,  and  so  meats*  that  have  been  cooked  and  milk 
that  has  been  Pasteurized  or  scalded  will  keep  longer  than 
they  do  when  left  uncooked.  If  meats,  vegetables,  or  fruits 
are  heated  to  the  boiling  point  in  cans  and  sealed  up  at 
once,  they  may  be  permanently  prevented  from  spoiling. 

Ham  and  herring  are  often  smoked  to  preserve  them, 
while  pork  and  codfish  are  soaked  in  a  strong  solution  of 
salt  (brine)  to  keep  them  from  the  decaying  action  of  bacteria. 
Another  method  of  preserving'  food  is  by  depriving  it  of 
water.  Dried  beef,  apples,  hay,  and  seeds  will  keep  indefi- 
nitely if  no  moisture  is  allowed  to  get  to  them.  Previous 
to  the  passage  of  the  Pure  Food  Law  by  Congress  in  1906, 
many  unscrupulous  dealers  were  accustomed  to  use  borax, 
formaldehyde,1  and  other  chemicals  to  prevent  their  food 
supplies  from  spoiling.  Fortunately  for  the  health  of  the 
consumer,  this  method  of  food  preservation  has  been  largely 
stopped  by  the  enforcement  of  the  law  to  which  we  have 
just  referred. 

1  Method  of  determining  whether  or  not  formalin  has  been  added 
to  milk.  Into  each. of  two  test  tubes  or  flasks  put  an  equal  quantity  of 
fresh  milk.  To  one  of  the  glasses  add  a  drop  or  two  of  formaldehyde 
solution.  Then  to  each  add  a  volume  of  hydrochloric  acid  equal  to 


MICROORGANISMS  AND  HUMAN   WELFARE         25 

23.  To  determine  the  best  method  of  cleaning  a  room. —  (Optional 
Demonstration . ) 

Select  three  rooms  with  rugs  or  carpets  as  nearly  as  possible  of  the 
same  size  and  amount  of  dirt.  Open  Petri  dish  No.  15  and  expose 
its  surface  for  five  minutes  at  the  level  of  the  table  while  one  of 
the  three  rooms  is  being  swept  with  a  broom.  In  a  similar  man- 
ner expose  the  surface  of  dish  No.  16  for  five  minutes  to  the  air  in  a 
room  that  is  being  cleaned  with  a  carpet  sweeper,  and  dish  No.  17 
in  the  third  room  for  five  minutes  while  it  is  being  cleaned  with  a 
vacuum  cleaner.  Close  each  of  the  dishes,  label,  and  put  in  a  warm 
place  (90°  to  100°  F.)  for  several  days. 

1.  Describe  the  preparation  of  dishes  15,  16,  and  17. 

2.  What  difference  do  you  find  in  the  relative  number  of  bacteria 

colonies  in  the  three  dishes  ? 

3.  What  do  you  conclude,  therefore,  as  to  the  most  effective  method 

of  removing  dust  and  germs  from  a  room  ? 

24.  Proper  methods    of   sweeping    and   dusting.  —  From 
our  experiments  (13,  23)  we  have  learned  that  large  num- 
bers of  bacteria   are   present   in  the   air  of  rooms  where 
dust  is  raised  by  the  movement  of  people  or  by  sweeping. 
Since  each  colony  started  from  a  single  bacterium,  it  is  easy 
to  show  the  relative  number  of  germs  present  in  the  air  under 
varying  conditions  (Fig.  11). 

The  number  of  bacteria  that  may  be  found  in  a  church, 
schoolroom,  theater,  or  living  room  has  been  proved  by  a 


that  of  the  milk  and  a  drop  of  ferric  chloride  (made  by  dissolving  a 
spoonful  of  ferric  chloride  in  a  quart  of  water).  Put  both  dishes  of 
milk  into  a  dish  of  boiling  water  and  stir  or  shake  frequently  for 
five  minutes. 

1.  Describe  the  preparation  of  the  experiment. 

2.  At  the  end  of  five  minutes  state  the  color  produced  in  the  milk 

in  each  of  the  two  test  tubes. 

3.  How,  then,  can  you  determine  whether  or  not  formalin  has  been 

added  to  milk? 


26  HUMAN  BIOLOGY 

long  series  of  experiments  to  be  enormous,  for  with  the  or- 
dinary methods  of  "  cleaning  "  these  rooms,  very  few  of 
the  germs  are  removed.  When  a  room  is  swept,  most  of 
the  light  dust  particles  are  raised  from  the  floor  and  mingled 
with  the  air.  After  a  short  time  the  room  is  "  dusted," 
often  with  a  feather  duster.  The  bacteria  which  may  have 
settled  are  whisked  off  again  into  the  air.  Experiments 
have  shown,  too,  that  the  number  of  germs  in  a  room  is 
not  materially  diminished  by  ventilating  currents,  unless 
there  is  a  strong  draught. 

Most  of  this  germ  dust  can,  however,  be  removed  from 
our  homes  if  they  are  cleaned  in  a  proper  manner.  In  a  room 
that  has  not  been  used  for  three  or  four  hours  practically  all 
of  the  bacteria  and  fine  dust  particles  have  settled  out  of 
the  air  upon  the  horizontal  surfaces.  For  dusting,  a  cloth 
should  always  be  used.  "  Dustless  dusters  "  may  be  bought 
or  prepared  by  soaking  a  piece  of  cheesecloth  or  flannel  in 
a  mixture  of  wax  and  turpentine,  or  by  slightly  sprinkling 
cheesecloth  with  water.  By  the  use  of  these  cloths  most  of 
the  particles  of  dirt  may  be  taken  up  and  then  removed  from 
the  cloths  by  washing.  If  carpets,  rugs,  and  draperies  are 
then  cleaned  with  a  vacuum  cleaner,  practically  no  dust  is 
raised  (Fig.  11) ;  hence,  further  dusting  is  unnecessary. 
Careful  investigation  has  demonstrated  that  the  use  of  a 
vacuum  cleaner  on  surfaces  that  may  be  washed  or  wiped 
with  a  cloth  is  too  expensive  a  method  of  cleaning,  and  that 
it  is  not  nearly  as  effective. 

It  is  much  more  hygienic  to  have  floors  covered  with  rugs, 
for  if  a  vacuum  cleaner  is  not  available,  the  dusty  rugs 
and  draperies  may  be  removed  from  the  room  and  cleaned  in 
the  open  air.  In  general,  a  carpet  sweeper  is  to  be  preferred 
to  a  broom  as  a  means  of  cleaning  carpets,  since,  as  Fig.  1 1 
shows,  fewer  germs  are  stirred  up  when  the  former  is  used. 


MICROORGANISMS  AND  HUMAN   WELFARE          27 


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28 


HUMAN  BIOLOGY 


If  brooms  are  used,  small  pieces  of  crumpled  newspapers  or 
tea  leaves  should  be  moistened  and  scattered  on  the  floor 
before  the  sweeping  is  done.1 

In  cleaning  public  buildings,  the  floors  should  first  be 
sprinkled  with  moist  sawdust  and  then  the  coarser  dirt 
collected  by  brushing  with  hair  brooms.  The  floors  should 
then  be  washed  each  day  if  possible.2  Dirty  streets,  too, 
are  a  constant  source  of  dust  infection.  Most  of  the  irrita- 
tion and  possible  diseases  from  this  source  would  be  avoided, 

1  Figure  1 1  shows,  so  far  as  bacteria  are  concerned,  the  compara- 
tive results  obtained  by  four  methods  of  sweeping.  Four  rugs  of 
the  same  size  and  approximately  the  same  amount  of  use  were 
selected,  and  placed  at  night  in  four  different  rooms.  Early  the 
next  morning  a  Petri  dish  was  uncovered  in  each  room,  and  thus 
the  nutrient  agar  of  each  dish  was  exposed  to  the  air  of  the  room 
for  five  minutes  ;  after  which  the  dishes  were  covered. 

A  second  set  of  four  dishes  was  then  opened  in  turn  for  five  min- 
utes while  the  four  rugs  were  being  cleaned  as  follows.  Rug  D  was 
swept  with  a  dry  broom;  rug  C  was  covered  with  pieces  of  wet 
newspaper  and  then  swept  with  a  broom ;  rug  B  was  cleaned  with 
a  carpet  sweeper ;  and  rug  A  was  cleaned  with  a  vacuum  cleaner. 

All  of  the  eight  dishes  were  then  closed  and  kept  in  a  warm  room 
for  five  days  and  at  the  end  of  that  time  were  photographed.  (See 
Fig.  11.)  The  number  of  bacteria  colonies  in  each  dish  were  counted, 
and  the  results  are  expressed  in  the  following  table  : 


No.  COLONIES 
BEFORE  SWEEPING 

No.  COLONIES 
AFTER  SWEEPING 

No.  TIMES  COLONIES 
WERE  INCREASED  BY 
SWEEPING 

DishD     .... 

4 

1190 

297+ 

Dish  C      .     .     .     . 

6 

436 

72+ 

DishB      .... 

7 

135 

19+ 

Dish  A      .... 

25 

118 

4+ 

Hence  over  four  times  as  many  bacteria  were  stirred  up  by  a  car- 
pet sweeper  as  by  a  vacuum  cleaner,  eighteen  times  as  many  when 
the  sweeping  was  done  with  a  broom  and  wet  paper,  and  over  seventy 
times  as  many  when  a  dry  broom  was  used. 

2  We  are  indebted  to  Mr.  John  H.  Federer,  Superintendent  of  the 
New  York  Public  Library  building,  for  valuable  information  con- 
tained in  the  preceding  paragraphs. 


MICROORGANISMS  AND  HUMAN   WELFARE 


29 


however,  if  the  citizens  insisted  that  the  streets  be  kept 
watered,  especially  when  they  are  swept.  Street  sweeping 
and  the  removal  of  garbage  should  be  done  as  far  as  possible 
at  night/ 

25.  Treatment  of  cuts.  —  A  vast  amount  of  discomfort 
and  possible  danger  from  bacterial  infection  in  the  body 
would  be  avoided  if  people  but  used  proper  care  in  the  treat- 
ment of  wounds.  We  have  seen  that  white  corpuscles 
resemble  amoebae  in  their  structure  and  activities  (7).  Let 
us  now  study  their  functions 
in  the  human  body.  When 
one  gets  a  sliver  of  wood  in 
one's  finger  and  leaves  it  there 
for  a  time,  the  finger  becomes 
more  or  less  swollen  and  sore, 
and  white  "  matter  "  or  pus 
usually  forms  in  the  region  of 
the  wound.  These  effects  are  ~White  <*>n>uscleB. 

principally  due  to  the  activity  0^Jite  corpuscle  devourin*  a  ^ 
of  bacteria,  which  were  car- 6^iawhite  corpuscle  destroyed  by  bac~ 
ried  into  the  wound  on  the 

piece  of  wood.  Finding  in  the  tissues  all  the  favorable 
conditions  for  growth,  these  minute  organisms  multiply 
rapidly  and  produce  poisons  called  toxins,  that  cause  the 
inflammation. 

As  soon  however,  as  these  inflammatory  processes  begin, 
large  numbers  of  white  corpuscles  are  hurried  to  the  spot 
and  proceed  to  attack  the  invading  bacteria.  If  the  number 
of  germs  is  relatively  small,  and  if  the  corpuscles  are  in  a 
healthy  condition,  these  cells  of  the  blood  seize  upon  and 
devour  the  bacteria  (Fig.  12)  in  the  same  way  that  an  amceba 
takes  in  its  food.  Under  these  conditions  little  if  any 


30 


HUMAN  BIOLOGY 


pus  is  formed.     But  if  the  bacteria  get  the  upper  hand  in 
the  struggle,  many  of  the  corpuscles  are  killed,  and  it  is  the 

dead  white  cor- 
puscles that  form 
the  pus. 

In  case  of  a  cut 
the  wound  should 
be  cleansed  as 
quickly  as  pos- 
sible with  peroxid 
of  hydrogen  or 
some  other  germ- 
destroying  solu- 
tion, and  should 
then  be  covered 
with  absorbent 
cotton  soaked 
in  the  peroxid 
solution  and 
bandaged,  to 
prevent  the  en- 
trance of  other 
germs.  If  this 
is  not  done, 
bacteria  are 
likely  to  settle  in 
Courtesy  of  Dodd,  the  wound,  and 
healing  may  be 
delayed  or  even  more  serious  results  may  follow.  With 
proper  treatment  a  wound  should  show  no  signs  of  inflam- 
mation, or  formation  of  pus,  and  should  heal  rapidly. 

26.    The  cause   of    tuberculosis.  —  It  is   said    that    one 
seventh  of  all  the  deaths  in  the  world  are  due  to  the  disease 


FIG.  13.  —  Dr.  Robert  Koch,  German  bacteriologist. 
Born  1843.    Died  1910. 

(From    International    Encyclopedia. 
Mead  &  Co.). 


MICROORGANISMS  AND  HUMAN   WELFARE 


31 


tuberculosis,  which  is  more  commonly  known  as  consump- 
tion. In  New  York  City  alone  the  Board  of  Health  reports 
300  to  400  new  cases  every  week.  Yet  if  the  general  public 
only  knew  the  manner  in  which  this  disease  is  transmitted 
and  would  make  use  of  this  knowledge,  the  dreadful  sacrifice 
of  life  and  health  due  to  this  "  great  white  plague  "  could  be 
almost  wholly  prevented. 

It  was  conclusively  proved  in  1882  by  Dr.  Koch,  a  noted 
German  scientist  (Fig.  13), that  tuberculosis  is  always  caused 
by  extremely  small,  rod-shaped  bacteria,  bacillus  tuberculosis 
(Fig.  14) .  He  found  countless  numbers  of  these  living  germs 
in  the  sputum  coughed  up 
by  consumptive  patients; 
he  cultivated  these  germs 
in  test  tubes  and  when  he 
injected  the  bacteria  into 
the  bodies  of  guinea  pigs 
or  rabbits,  the  animals  be- 
came ill  with  tuberculosis. 
By  many  experiments  of 
this  sort,  biologists  have 
learned  important  facts  in 
regard  to  the  cause,  preven- 
tion, and  cure  of  disease. 

We  are  absolutely  sure 
then,  that  before  any  one 
can  become  a  consumptive,  he  must  take  into  his  body  the 
living  bacteria  of  consumption,  and  the  most  common  avenue 
of  infection  is  through  the  nose  and  air  passages.  Consump- 
tives who  are  ignorant  of  the  danger  they  are  causing,  fre- 
quently expectorate  on  the  floors  of  rooms  or  of  public  con- 
veyances, and  when  this  sputum  becomes  dried,  the  germs 
are  likely  to  be  blown  about  in  the  air,  and  to  be  inhaled  by 


FIG.  14.  — Tuberculosis  bacteria  in  human 
sputum.  (Courtesy  of  Dr.  Thomas  S. 
Carrington.) 


32  HUMAN  BIOLOGY 

other  people.  When  the  bacteria  get  into  the  lungs  of  a  per- 
son who  happens  to  be  a  little  "run  down,"  as  we  say, 
straightway  the  bacteria  begin  to  multiply,  feeding  meanwhile 
on  the  lung  tissues ;  for  this  reason  the  disease  is  called  con- 
sumption, and  if  it  is  not  arrested,  the  lungs  may  be  almost 
destroyed,  and  death,  of  course,  results.  During  the  progress 
of  the  disease,  little  masses  or  tubercles  of  lung  tissue 
(whence  the  name  tuberculosis)  are  thrown  off  by  the  patient 
in  coughing,  and  these,  as  we  have  already  stated,  are  swarm- 
ing with  living  bacteria. 

27.  The  prevention  of    tuberculosis.  —  It  is  of    the    ut- 
most importance,  therefore,  that  these  living  germs  be  kept 
out  of  the  bodies  of  people  who  come  in  contact  with  con- 
sumptives.    Responsibility  in  this  matter  rests  very  largely 
upon  the  patients  themselves,  and  if  they  exercise  the  neces- 
sary care,  they  need  not  become  a  menace  to  healthy  people 
in  the  home  or  in  the  community.     It  is  of  course  essential 
that  every  effort  be  made  to  stop  altogether  the  dirty  and  dan- 
gerous habit  of  spitting.     Many  people  have  the  disease  long 
before  they  are  aware  of  it,  and  a  general  public  sentiment 
should  be  developed  that  will  actively  assist  boards  of  health 
in  enforcing  their   rules   against   the  "spitting  nuisance." 
Every  consumptive  should  provide  himself  with  paper  cups 
or  cloths  that  may  be  burned,  together  with  their  contents. 

Tuberculous  patients  should  exercise  care  not  to  cough 
or  sneeze  without  covering  the  mouth  or  nose  with  a  hand- 
kerchief, for  it  has  been  proved  that  living  germs  are  widely 
distributed  by  carelessness  in  this  regard.  Separate  knives, 
forks,  spoons,  and  drinking  vessels,  which  ought  to  be  cleaned 
in  boiling  water,  should  be  set  apart  for  consumptives.  Kiss- 
ing the  lips  of  consumptives  should  never  be  permitted. 

28.  The   cure   of    tuberculosis.  —  In    former   years    the 
decision  by  doctors  that  a  patient  had  tuberculosis  was  be- 


MICROORGANISMS  AND  HUMAN    WELFARE 


33 


lieved  to  be  a  sentence  to  a  lingering  death ;  it  was  believed 
also  that  the  disease  was  hereditary.  Happily  modern 
medicine  has  dispelled  both  these  beliefs.  A  child  may 
inherit  weak  lungs  or  a  frail  body;  but  it  will  never  be  a 


A.   Tent  open. 
FIG.  15.  —  Window  tent. 


B.   Tent  closed. 
(Courtesy  of  Dr.  Thomas  S.  Carrington.) 


consumptive  unless  the  bacteria  that  cause  this  disease  are 
in  some  way  planted  in  his  tissues.  Consumption,  too,  is  a 
curable  disease,  unless  it  is  neglected  until  it  has  reached 
an  advanced  stage.  The  prime  requisites  in  the  treatment  of 
the  disease  are  a  plentiful  supply  of  fresh  air,  plenty  of  easily 


34  HUMAN  BIOLOGY 

digested  and  nutritious  food,  like  eggs  and  milk,  sleep  and 
freedom  from  hard  muscular  work  and  from  worry.  These 
conditions  may  be  obtained  even  in  crowded  cities,  for  by 
the  use  of  tents  on  the  roof,  or  of  window  tents  (Fig.  15)  a  suffi- 
cient amount  of  air  may  be  secured,  and  almost  marvelous 
cures  are  found  to  result.1 

29.  The   cause   and  treatment   of   pneumonia.  —  Another 
disease  that  affects  the  lungs  is  pneumonia.     It  is  more 
prevalent  in  the  spring  and  autumn  of  the  year,  and  is 
commonly  a  disease  of  adults.     The  cause  of  pneumonia  is  a 
spherical  form  of  bacteria,  which  get  into  the   lung  tissue 
and  grow  there  when  the  individual  is  physically  weak  or 
mentally    depressed.     Formerly,  in     treating    the    disease, 
patients  were  kept  in  closed  rooms,  carefully  shielded  from 
all  draughts  of  air.     It  has  been  found,  however,  as  is  the 
case  with  tuberculosis,  that  fresh  outdoor  air  is  one  of  the 
best  means  of  treating  the  patient.     To  combat  both  tuber- 
culosis and  pneumonia,  our  bodies  and  minds  should  be  kept 
in  such  a  healthy  and  vigorous  condition  that  invading  dis- 
ease germs  will  always  meet  with  a  hostile  reception  whenever 
they  attempt  to  prey  upon  our  organs  and  tissues. 

30.  Cause  of  diphtheria.  —  Another  disease  that  formerly 
claimed  many  victims  among  young  children  is  diphtheria. 
The  germs  of  this  disease  are  rod-shaped  organisms  some- 
what larger  than  those  that  cause  tuberculosis.     When  these 
bacteria  find  lodgment  and  grow  in  the  throat,  they  produce 
a  membrane  and  form  poisonous  substances  known  as  toxins, 
which  are  absorbed  and  carried  by  the  blood  to  other  parts  of 
the  body,  often  causing  paralysis  and  other  injurious  effects. 

1  The  authors  are  much  indebted  to  Dr.  Thomas  Spees  Carrington 
for  suggestions  relating  to  tuberculosis.  For  additional  suggestions 
see  Dr.  Carrington's  "  Fresh  Air  and  How  to  Use  It  "  ($  1),  National 
Association  for  the  Study  and  Prevention  of  Tuberculosis,  105  E. 
22d  St.,  New  York  City. 


MICROORGANISMS  AND  HUMAN    WELFARE         35 

31.  Treatment  of  diphtheria.  —  But  these  germs  do  not 
have  things  all  their  own  way.  The  cells  of  the  body  seem 
to  know  when  an  army  of  this  enemy  has  entered  their  terri- 
tory, and  they  at  once  set  to  work  to  produce  substances 
that  will  neutralize  or  overcome  the  toxins  formed  by  the 
diphtheria  bacteria;  these  substances  are  known  as  anti- 
toxins. When  the  disease  is  at  its  height,  there  is  a  fierce 
battle  between  the  invading  microbes  with  their  toxins  and 
the  cells  of  the  body  fighting  for  their  lives  by  means  of 
their  antitoxins.  If  the  bacteria  are  victorious,  death  ensues. 

In  the  year  1892  a  most  important  discovery  was  made  by 
a  German  bacteriologist  named  Von  Behring.  He  found 
that  it  is  not  necessary  for  the  human  body  to  manufacture 
all  the  antitoxin  it  needs  for  its  struggle  with  the  diphtheria 
poisons,  but  that  this  substance  may  be  taken  from  the  blood 
of  other  animals  that  have  produced  it.  For  this  purpose, 
healthy  horses  are  now  secured  by  city  boards  of  health,  and 
a  small  dose  of  diphtheria  toxin  is  injected  into  their  bodies; 
the  next  day  a  larger  dose  may  be  given  with  little  or  no  ill 
effects ;  until,  at  the  end  of  several  months  of  this  treatment, 
the  animals  can  stand  a  quantity  of  the  poison  that  would 
have  proved  fatal  if  given  at  an  earlier  time.  For  during 
all  these  days  the  horse  has  been  having  a  very  mild  form 
of  diphtheria,  and  the  cells  of  his  body  have  been  producing 
and  giving  into  the  blood  an  amount  of  antitoxin  much  more 
than  is  needed  to  neutralize  the  diphtheria  poisons  the  ani- 
mal has  received.  Some  of  the  blood  is  then  carefully  re- 
moved and  allowed  to  clot.-  The  liquid  serum  that  oozes 
out  of  the  clot  contains  the  antitoxin,  which  is  carefully 
prepared  for  injection  into  the  body  of  human  beings  when 
diphtheria  attacks  them.  And  so  our  good  friend  the  horse, 
without  any  permanent  ill-effects  to  himself,  has  decreased  the 
death  rate  formerly  caused  by  diphtheria  by  75  to  80  per  cent. 


36  HUMAN  BIOLOGY 

32.  Prevention  of  diphtheria.  —  We  have  learned  some- 
thing of  the  means  by  which  we  can  combat  this  disease 
when  once  it  has  begun  its  attack.     Antitoxin  may  also  be 
administered  to  any  members  of  the  family  who  have  been 
exposed  to  diphtheria,  and  it  then  becomes  a  means  of  pre- 
venting the  disease.     But  it  is  much  more  important,  as  is 
the  case  with  tuberculosis,  to  prevent  all  danger  from  attacks 
by  this  disease  than  it  is  to  know  how  to  cure  it.     Here  again 

we  find  strong  arguments  for  the  enforce- 
ment of  the  rules  against  spitting,  for  liv- 
ing bacteria  are  often  found  in  the  throats 
of  sufferers  from  what  are  thought  to  be 
ordinary  sore  throats.  For  this  reason, 

FlG'  btcterIayPh°id     too>  children  should  be  especially  careful 

to  avoid  putting  into  their  mouths  pencils, 

coins,  candies,  or  other  objects  that  have  been  used  by  other 

pupils,  for  diphtheria  germs  have  been  frequently  transmitted 

in  this  manner. 

33.  Cause  of  typhoid  fever.  —  Typhoid  fever  is  a  disease 
caused  by  the  growth  in  the  tissues  of  the  intestines  of  rod- 
shaped  bacteria.     The  typhoid  bacteria  have  several  hair- 
like  projections  something  like  long  cilia  (known  as  flagelld), 
which  vibrate  rapidly  and  so  enable  the  germs  to  move  about 
(Fig.  16).     These  bacteria  are  practically  always  taken  into 
the  body  through  the  mouth  and  thence  into  the  intestines. 
"  Food  and  drink  are  usually  the  vehicles  which  serve  for 
the  entrance  of  the  bacillus,  water  and  milk  being  probably 
the  most  frequent  sources  of  infection.     The  latter  is  es- 
pecially dangerous  from  the  fact  that  the  typhoid  bacillus 
not  only  lives  but  multiplies  in  it.     Water  and  milk,  however, 
are  only  dangerous  when  they  actually  contain  the  typhoid 
bacilli  which  have  entered  into  them  from  the  excretions  of 


MICROORGANISMS  AND  HUMAN   WELFARE         37 

typhoid  patients  or  those  who  have  become  typhoid  car- 
riers." l  It  has  been  proved  over  and  over  again  that  the 
common  house  fly  is  frequently  the  means  by  which  typhoid 
fever  is  transmitted  (A.  B.,  43),  since  these  insects  often 
alight  on  the  excretions  of  typhoid  patients,  and  then  carry 
the  germs  on  their  hairy  feet  (A.  B.,  Fig.  40),  and  so  infect 
the  foods  on  which  they  alight. 

34.  Prevention  of  typhoid  fever.  —  It  is  evident,  then, 
that  if  the  excretions  from  the  intestines  and  kidneys  of 
typhoid  patients  were  thoroughly  disinfected  by  carbolic 
acid  or  other  germicides,  the  spread  of  typhoid  fever  would 
be  very  largely  prevented.  It  must  be  borne  in  mind, 
however,  that  the  bacteria  of  this  disease  continue  to  live 
in  great  numbers  and  to  multiply  in  the  intestines  of  some 
people  who  have  had  typhoid  fever  years  after  recovery  from 
the  disease,  and  these  people  are  the  so-called  "  typhoid 
carriers."  2 

One  of  the  most  difficult  problems  that  formerly  confronted  armies 
was  that  of  preventing  typhoid  infection.  In  the  Mexican  War  and 
in  the  Civil  War  the  armies  on  both  sides  paid  frightful  toll  to  this 
dread  disease,  and  even  in  the  Cuban  War,  five  thousand  men  in  the 
United  States  Army  died  of  typhoid  fever  or  other  fly-borne  dis- 
eases, while  only  three  hundred  were  killed  by  Spanish  bullets. 
Sanitary  camps,  however,  have  greatly  improved  the  situation,  and 
in  recent  years  an  anti-typhoid  vaccine,  somewhat  like  that  used  in 
the  prevention  of  smallpox,  is  injected  as  a  means  of  prevention, 
and  the  results  of  the  use  of  this  vaccine  have  been  most  favorable. 
The  improvement  in  army  health  is  strikingly  shown  by  comparing 
figures  for  two  army  divisions  of  about  the  same  size,  one  at  Jack- 
sonville, Florida,  during  the  Spanish-American  War  in  1898,  the 

1  Quoted  from  article  on  typhoid  fever,  in  New  International  En- 
cyclopedia, copyrighted  1903  by  Dodd,  Mead,  and  Co. 

2  See  footnote,  p.  39. 


38 


HUMAN  BIOLOGY 


other  at  San  Antonio,  Texas,  during  the  1911  maneuvers  on  the 
Mexican  border. 


JACKSONVILLE 
1898 

SAN  ANTONIO 
1911 

Number  of  soldiers  

10,759 

12,801 

Number  cases  typhoid  (certain  and 
probable) 

2693 

1 

Number  of  deaths  from  typhoid  fever 
Number  of  deaths  from  all  diseases  .     . 

248 
281 

0 
11 

35.  Water  supplies.  —  In  country  districts    each   house 
usually  has  its  own  well,  and  so  the  family  becomes  account- 
able for  its  own  water  supply.     In  this  case  great  care  should 
be  taken  to  place  the  well  in  such  a  position  that  none  of 
the  drainage  from  the  house  or  barn  can  soak  through  the 
soil  into  the  well-water.      Those  who  live  in  large  towns 
and  cities  almost  always  obtain  their  water  supply  from  a 
common   source.     This    sometimes    becomes    contaminated 
by  typhoid  and  other  germs,  and  a  disease  epidemic  then 
follows.     Hence,  if  there  is  any  doubt  as  to  the  purity  of  a 
water  supply,  boards  of   health  should   notify  the  house- 
holders, and  the  water,  when  used  for  drinking  purposes, 
should  then  be  boiled  and  kept  in  bottles  on  ice  until  used. 

36.  Milk  supplies.  —  Many  families  in  rural  communities 
keep  their  own  cows,  and  so  they  can  be  sure  of  clean  milk 
if  they  only  take  the  necessary  trouble.     Cows,  like  human 
beings,  need  plenty  of  light,  air,  wholesome  food,  and  clean 
surroundings.     If  any  of  these   are  wanting,   the   animals 
are  likely  to  become  diseased,  and  the  milk  is  then  affected. 
Great  care  should  be  taken  also  at  milking  time  to  see  that 


MICROORGANISMS  AND  HUMAN   WELFARE          39 

the  surface  of  the  body  of  the  cow,  especially  about  the 
flanks  and  udder,  are  brushed  and  wiped  with  a  moist  cloth, 
and  that  the  hands  and  clothing  of  those  who  milk  are  kept 
clean;  otherwise  enormous  numbers  of  microbes  will  fall 
into  the  milk.  No  one  who  has  any  infectious  disease  should 
be  allowed  to  have  anything  to  do  with  the  care  of  cows  or 
of  milk  until  he  has  completely  recovered.  Over  and 
over  again  epidemics  of  diphtheria,  scarlet  fever,  typhoid,1 
and  tuberculosis  in  infants  have  been  traced  along  the  routes 
of  careless  milkmen. 

Those  who  live  in  cities,  however,  are  wholly  dependent 
for  milk  upon  sources  they  know  nothing  about.  The  milk 
that  is  consumed  in  New  York  City,  for  instance,  comes  from 
over  40,000  dairies  scattered  through  six  different  states. 
It  is,  of  course,  impossible  to  make  any  proper  inspection  in 
such  a  wide  field.  The  New  York  Board  of  Health  is  doing 
all  it  can  in  this  respect,  and  so  far  as  possible  it  prevents 
dirty  and  dangerous  milk  from  coming  to  the  city.  The 
only  path  of  safety,  however,  lies  in  the  careful  Pasteuriza- 
tion of  milk  and  cream  that  are  used  for  drinking  purposes, 
especially  by  young  children.  In  communities  where  Pas- 
teurization has  been  tried  at  all  generally,  there  has  been  a 
surprising  decrease  in  the  percentage  of  sickness  and  death 
from  intestinal  diseases,  especially  in  the  summer  time  and 
among  young  children.  The  instruction  given  by  boards 
of  health  to  mothers  and  to  older  children  as  to  the  care  of 
the  young  during  the  hot  months  has  also  helped  to  save  the 
lives  of  a  large  number  of  infants. 

1  A  sudden  increase  in  the  number  of  cases  of  typhoid  fever  in 
New  York  City  in  1909  was  found  to  be  entirely  due  to  milk  fur- 
nished by  a  dairyman  in  a  town  in  New  York  State.  He  had  re- 
covered from  typhoid  fever  in  1864,  but  still  carried  infection  in 
his  body  and  passed  an  enormous  number  of  the  germs  of  the  dis- 
ease. 


40 


HUMAN  BIOLOGY 


37.  Smallpox  and  vaccination.  —  Smallpox  was  once  so  common 
that  scarcely  one  person  in  a  hundred  escaped  it.  It  was  intro- 
duced into  America  by  the  Spaniards,  it  destroyed  3,500,000  people 
in  Mexico,  and  spread  with  frightful  rapidity  throughout  the  New 

World,  until  in 
1733  it  nearly  de- 
populated Green- 
land. Mankind  is 
indebted  to  Dr. 
Edward  Jenner 
(Fig.  17),  an  Eng- 
lish physician,  who 
in  1796  proved 
that  vaccination  is 
a  sure  method  of 
preventing  the  dis- 
ease. In  vaccina- 
tion our  bodies  re- 
ceive germs  that 
originally  came 
from  smallpox,  but 
which  have  been 
so  modified  that 
they  cause  a  mild 
form  of  disease 
very  different  from 
smallpox  itself. 
The  cells  produce 

(From   International  Enclyclopedia.    Courtesy   of    Dodd,        some  form  of  anti- 
Mead  &  Co.). 

toxin  which  is  ef- 
fective protection  when  we  are  exposed  to  the  disease.  This  kind 
of  protection  does  not  last  indefinitely,  however,  and  every  person 
should  make  sure  that  successful  vaccination  is  performed  at  least 
once  in  ten  years,  and  oftener  than  that  if  cases  of  smallpox  develop 
in  the  community  in  which  he  is  living.  If  a  person  has  been  act- 
ually exposed  to  the  disease,  he  should  be  vaccinated  immediately. 


FIG.  17. —  Dr.  Edward  Jenner,  English  physician. 
Born  1749.     Died  1823. 


MICROORGANISMS  AND  HUMAN    WELFARE  41 

Since  the  introduction  of  compulsory  vaccination,  smallpox  is  be- 
coming very  rare. 

38.  Hydrophobia  and  the  Pasteur  treatment.  —  Hydrophobia,  or 
rabies,  is  a  disease  due  to  the  bite  of  a  mad  dog,  cat,  or  wolf.    Until 
the  latter  part  of  the  nineteenth  century  the  only  known  method  of 
treating  this  disease  was  that  of  burning  out  or  cauterizing  the 
wounds  with  hot  irons  or  nitric  acid.     After  a  long  series  of  investi- 
gations, however,  Louis  Pasteur  (Frontispiece),  a  French  scientist, 
made  known  to  the  world  the  so-called  Pasteur  treatment  (1885). 
Pasteur  found  that  the  disease  was  located  in  the  spinal  cord,  and 
that,  if  pieces  of  the  spinal  cord  of  a  rabbit  which  had  died  of  hy- 
drophobia are  allowed  to  dry  in  the  air,  the  germs  gradually  lost 
their  virulence.     He  therefore  began  the  treatment  of  patients  who 
had  been  bitten  by  mad  dogs  by  first  injecting  beneath  the  skin  an 
emulsion  made  from  the  spinal  cords  which  had  been  dried  for  four- 
teen days.     Each  day  for  twenty-one  days  an  injection  was  made 
from  a  cord  that  had  been  dried  for  a  shorter  time.     Since  hydro- 
phobia usually  does  not  develop  in  human  beings  for  two  weeks  to 
four  months  after  the  bite  of  a  mad  dog,  the  cells  of  the  body  by 
this  Pasteur  treatment1  gradually  acquire  the  power  to  resist  the 
hydrophobia  toxins,  and  so  the  disease  is  prevented,  if  the  wound 
is  cauterized  at  once  and  treatment  begun  immediately.     The  cau- 
terization is  of  value  even  after  a  delay  of  twenty-four  hours.1 

39.  The  cause  and  prevention  of  other  diseases.  —  The 
germs  that  cause  scarlet  fever,  yellow  fever,  measles,  whoop- 
ing cough,  and  infantile  paralysis  have  not  as  yet  been  dis- 
covered.    Since,  however,  they  are  all  infectious  diseases  like 
tuberculosis  and  diphtheria,  they  must  be  due  to  some  form 
of  microbe.     Those  in  yellow  fever,  measles,  and  infantile 
paralysis  are  so  small  that  they  pass  through  stone  niters. 

1  The  authors  are  much  indebted  to  Dr.  W.  H.  Park,  Director  of 
the  Laboratory  of  the  Board  of  Health  of  New  York  City,  for  his 
suggestive  criticism  of  the  sections  relating  to  disease-producing  bac- 
teria. 


HUMAN  BIOLOGY 


These  cells  are  therefore  too  small  to  be  seen  by  the  most 
powerful  microscopes. 

The  life  history  and  method  of  transmission  of  the  micro- 
scopic animal  that  causes  malaria  has  already  been  dis- 
cussed in  connection  with  the  study  of  the  Anopheles 
mosquito  (A.  B.,  40).  Likewise,  it  has  been  demonstrated 
beyond  a  cavil  that  infection  from  a  yellow-fever  patient  can 
only  be  brought  about  through  the  agency  of  the  Stegomyia 
mosquito.  Hence,  to  eradicate  these  diseases  entirely,  we 
need  only  to  exterminate  all  Anopheles  and  Stegomyia  mos- 
quitoes. Sleeping  sickness  is  a  dread 
-cilia  disease  Of  the  tropics  which  is  due 
to  a  kind  of  Protozoan  something 
like  a  paramecium. 


mucous  cells  in  various  stages  of 
secretion 

FIG.  18.  —  Ciliated  cells  from 
the  windpipe. 


40.  Safeguards  of  the  body  against 
disease.  — •  In  the  first  place,  the 
tough  outer  skin,  as  long  as  it  is 
unbroken,  forms  a  most  effective 
barrier  to  the  entrance  of  bacteria, 
except  at  the  mouth  and  nose 
openings.  Each  of  the  nostrils  is 
guarded  by  hairs  that  collect  a  large 
number  of  dirt  particles.  On  the  mucous  membrane  lining 
the  nose  and  throat  still  other  bacteria  are  caught,  and  the 
cells  which  line  the  windpipe  are  furnished  with  cilia,  which 
lash  upward  (Fig.  18)  and  tend  to  expel  the  germs  that  may 
have  gone  past  the  outer  lines  of  defense  that  we  have  named. 
If  the  bacteria  enter  the  stomach  and  intestines  in  a  living 
condition,  many  of  them  are  digested  with  the  food.  And 
even  though  the  invading  microbes  finally  reach  the  interior 
of  the  cells  of  our  lungs,  or  muscles,  or  brain,  we  can  still 
rely  upon  the  antitoxins  which  the  cells  of  a  healthy  human 


MICROORGANISMS  AND  HUMAN   WELFARE          43 

body  are  ever  ready  to  produce.  In  the  case  of  many  of  the 
contagious  diseases,  like  scarlet  fever  or  smallpox,  these 
antitoxins  remain  for  a  considerable  time  in  the  blood  to 
make  us  immune  against  a  second  attack.  The  white  cor- 
puscles, too,  are  a  sort  of  cavalry  troop,  ready  to  pounce  upon 
the  bacteria  and  either  devour  them  or  carry  them  off  from 
the  body  (Fig.  12,  A).  An  optimistic  view  of  life  and  free- 
dom from  worry  are  undoubtedly  very  important  factors  hi 
keeping  the  body  in  a  state  of  vigorous  health. 

41.  Topics  for  biology  composition.1  —  Optional  Library 
Work.  Consult  the  local  health  authorities,  Allen's  "  Civics  and 
Health,"  Bulletins  of  U.  S.  Department  of  Agriculture,  New  Inter- 
national or  other  Encyclopedia,  and  other  sources,  and  prepare  in 
your  notebook  a  composition  on  one  or  more  of  the  following 
topics:  — 

1.  The  Work  of  the  Board  of  Health. 

2.  The  Work  of  the  Tenement  House  Commission. 

3.  How  a  City  May  Be  Kept  Clean. 

4.  A  Visit  to  a  Model  Dairy. 

5.  City  Milk  Inspection. 

6.  A  Hygienic  House. 

7.  Helpful  Bacteria. 

8.  City  Playgrounds  and  Parks  :  Their  Use  and  Abuse. 

9.  How  the  Study  of  Bacteria  Can  Help  Us  in  Our  Homes. 

10.  Sleeping  in  the  Open  Air. 

11.  A  Visit  to  Ellis  Island:    How  the  Commission  Cares  for 
Immigrants. 

12.  The  Responsibility  of  the  Individual  for  Public  Health. 

13.  An  Ideal  School  Infirmary. 

14.  The  Work  of  the  Consumers'  League. 

15.  Methods  of  Sewage  Disposal. 

16.  The  City  Water  Supply. 

1  The  authors  are  indebted  to  Miss  Edith  Read  of  the  Morris 
High  School  for  the  following  list  of  composition  topics. 


CHAPTER  III 

FOODS  AND   THEIR  USES 

I.  FOOD  SUBSTANCES  FOUND  IN  THE  HUMAN  BODY 

42.  Composition  of  the  body.  —  Many  careful  analyses 
have  been  made  of  the  composition  of  the  human  body,  and 
these  analyses  have  shown  that  our  bodies  are  made  of  the 
same  kinds  of  materials  as  those  found  in  plants ;  namely, 
proteins,  fats,  carbohydrates,  mineral  matters,  and  water. 

43.  Proteins.  —  The  most  important   substances  in   the 
living  body  are  the  proteins.     As  we  have  already  learned,1 
proteins  are  essential  constituents  of  the  protoplasm  of  every 
plant  cell,  and  this  is  likewise  true  of  the  cells  in  animal  and 
human  bodies. 

44.  Fats  and  carbohydrates.  —  The  amount  of  fat  in  the 
body  varies  greatly  in  different  individuals,  but  it  is  always 
present  in  some  quantity.     Muscle,  however  lean,  contains 
particles  of  fat;    fat  constitutes  a  small  percentage  of  the 
blood;  it  fills  the  spaces  in  the  interior  of  bones;  and  it  is 
often  deposited  in  considerable  quantity  in  the  deeper  layers 
of  the  skin.     In  the  blood  and  in  other  animal  tissues  we  find 
some  of  the  carbohydrate  called  grape  sugar.     Another  car- 
bohydrate known  as  animal  starch,  or  glycogen,  is  found  in  the 
liver  and  in  the  muscles. 

45.  Mineral   matters.  —  Mineral    matters    are    found    in 
the  greatest  quantities  in  the  bones  and  the  teeth.     When 

*43,  "Plant  Biology." 
44 


FOODS  AND   THEIR    USES  45 

we  burn  bones,  about  one  third  of  the  weight  disappears,  the 
remaining  two  thirds  being  bone  ash,  which  is  the  mineral 
matter.  Every  part  of  the  body,  however,  contains  some 
mineral  ingredients ;  for  when  muscle,  liver,  brain,  or  blood 
is  burned,  there  remain  some  traces  of  ash  in  each  case. 

46.  Water.  —  The  great  importance  of  water  in  the  com- 
position of  the  human  body  is  evident  from  the  fact  that  this 
compound  forms  about  62  per  cent  of  the  weight  of  an  adult. 
Hence,  if  all  the  water  were  removed  from  the  body  of  a  man 
weighing  one  hundred  and  fifty  pounds,  the  solids  that  re- 
mained would  weigh  less  than  sixty  pounds.     The  different 
organs  vary  greatly  in  their  percentages  of  water;  bones 
contain  about  22  per  cent,  muscles  have  75  per  cent,  and  the 
kidneys  82  per  cent. 

II.  THE  NECESSITY  FOR  FOODS 

47.  Necessity  of  foods  for  growth.  —  During  the  earlier 
years  of  life,  as  we  all  know,  the  human  body  rapidly  increases 
in  weight.     A  child  at  birth  usually  weighs  seven  to  eight 
pounds,  whereas  the  weight  of  a  fully  grown  man  is  often 
one  hundred  and  fifty  pounds  or  more.      Hence  during  a 
lifetime  there  is  often  a  twentyfold  increase  in  weight.     To 
provide  for  this  increase  or  growth  a  large  amount  of  new 
material  must  of  course  be  taken  in  by  the  human  being, 
and  this  material  is  supplied  by  the  food. 

48.  Necessity  of  foods  for  repair  and  for  the  production 
of  energy.  —  On  the  other  hand,  it  is  not  difficult  to  prove 
that  throughout  life  the  body  tends  constantly  to  decrease 
in  weight.     For  instance,   if  one  were  weighed  on  accurate 
scales  immediately  after  eating^  and  then  again  after  several 
hours  had  elapsed  and  before  food  or  drink  had  been  taken, 
a  decrease  in  weight  would  be  noted.     Still  more  striking  is 


46  HUMAN  BIOLOGY 

the  loss  of  weight  due  to  abstaining  from  food  because  of 
illness  or  other  reasons. 

It  has  been  found  too  that  when  one  is  engaged  in  very 
active  exercise,  such  as  playing  tennis  or  football,  the  loss 
of  weight  is  greater  than  when  one  remains  quiet.  How,  then, 
can  we  account  for  the  loss  of  weight  in  all  the  cases  that 
we  have  been  enumerating  ?  We  all  know  that  during  violent 
activity  considerable  quantities  of  perspiration  are  given 
off  from  the  skin,  and  this  has  been  proved  to  be  true  at  all 
other  times,  though  to  a  less  extent.  It  has  also  been  demon- 
strated that  many  waste  materials  are  given  off  from  the 
lungs,  the  organs  of  digestion,  and  the  kidneys. 

We  have  now  accounted  for  the  constant  loss  of  weight 
in  our  bodies,  but  we  have  still  to  ask  ourselves  how  these 
waste  substances  are  produced  in  the  body.  The  two 
commonest  wastes  of  the  body  are  carbon  dioxid  and  water. 
These  are  produced  by  the  oxidation  of  the  carbon  (P.  B.,  80) 
and  the  hydrogen  in  the  foods.  This  has  also  been  proved 
to  be  true  in  animals  and  in  the  human  body. 

49.  Definition  of    a  food.  —  The  three  most    important 
uses  of  foods  have  been  suggested  in  the  preceding  sections. 
Hence  we  may  say  that  a  food  is  any  substance  that  yields 
material  for  the  repair  or  growth  of  the  body,  or  that  supplies 
the  fuel  used  by  the  body  for  producing  heat,  or  power  to  do  work. 
It  should  be  understood,  however,  that  no  substance  should 
be  regarded  as  a  food  if  it  injures  the  body  while  supplying 
materials  for  growth,  repair,  or  the  production  of  energy. 

III.   THE  COMPOSITION  OF  FOODS 

50.  To  determine  the  food  substances  present  in  milk.  — 
Laboratory  demonstration. 

1.   Shake  a  bottle  containing  milk  and  cream  and  pour  a 


FOODS  AND   THEIR    USES  47 

small  amount  into  a  test  tube ;  add  a  little  strong 
nitric  acid,  and  boil. 

a.  Describe  what  was  done. 

b.  What  change  in  the  color  of  the  milk  do  you  observe  ? 

c.  What  food  substance  do  you  therefore  conclude  to  be 

present  in  milk? 

2.  Place  a  drop  of  the  "  mixed  milk/'  used  in  1  above,  on 

paper,  and  allow  the  paper  to  dry  over  a  warm 
radiator.  Hold  the  paper  to  the  light.  What  kind 
of  food  substance  is  present  in  considerable  quantity 
in  the  milk?  How  do  you  know? 

3.  Add  a  few  drops  of  iodine  to  some  milk.     What  is  the 

result,  and  what  is  your  conclusion? 

4.  Test  another  sample  of  milk  with  Fehling's  solution. 

State  the  result  and  your  conclusion  from  the  ex- 
periment. The  sugar  found  in  milk  is  known  as 
milk  sugar,  and  when  it  is  heated  with  Fehling's 
solution,  it  is  changed  to  grape  sugar. 

5.  Heat  a  half  spoonful  of  milk,  and  hold  over  it  a  clean, 

dry  tumbler.  What  nutrient  does  this  experiment 
prove  to  be  present?  Why? 

6.  (Optional.)     Evaporate  to  dryness  the  spoonful  of  milk,  and  then 

burn  the  solid  residue  over  a  very  hot  flame.  Does  all 
the  solid  disappear,  or  is  something  left  on  the  spoon? 
What  is  your  conclusion  as  to  the  presence  or  absence  of 
mineral  matter  in  milk  ? 

7.  As  a  conclusion  from  all  your  experiments,  state  what 

food  substances  or  nutrients1  are  present  in  milk, 
and  what  food  substances  are  absent. 

51.  The  composition  of  other  foods.  —  Our  study  of 
milk  has  shown  us  that  this  food  is  composed  of  the  same 

1  In  our  study  of  plant  biology  we  called  the  compounds  named  in 
this  paragraph  food  substances  rather  than  nutrients,  for  botanists 
regard  the  simpler  compounds  (carbon  dioxid,  water,  and  mineral 
matters)  that  plants  obtain  from  the  water  and  air  as  the  nutrients 
of  the  plants.  By  some  writers  water  is  not  regarded  as  a  nutrient ; 
since,  however,  it  is  an  essential  constituent  of  protoplasm,  it  may 
well  be  named  among  the  nutrients. 


48 


Protein:  1.CK 


HUMAN  BIOLOGY 

Fat:85.0 


5h:3.0 


WHITE  AND  YOLK 


Water:  61.9 


FIG.  19.  — Composition  of  common  animal  foods.     (Drawn  from  Charts  of  U.  S. 
Dept.  of  Agriculture  by  Mabelle  Baker.) 


FOODS  AND   THEIR    USES 


49 


Water:  35. 

Protein:  8. 

Carte- 

hydrates*.  JJ 


Fat:  4 


ater.83.0 


Fat;0,5 
,rbohy<ii'ates:l3.5 


Waten89.2 


Ash:1. 


CarboK/dratea:  18-4  Wafer:  763 


FIG.  20.  —  Composition  of  common  vegetable  foods.     (Drawn  from  Charts  of  U.  S. 
Dept.  of  Agriculture  by  Mabelle  Baker.) 


50  HUMAN  BIOLOGY 

kind  of  food  substances  that  we  found  in  plants;  and  this 
is  what  we  might  expect,  since  the  cow  is  wholly  dependent 
upon  grass  and  other  vegetable  foods.  Indeed,  when  we 
analyze  any  other  animal  foods  that  we  eat,  we  find  that  all 
consist  of  one  or  more  of  the  food  substances  which  closely  re- 
semble those  that  we  have  been  studying  in  plant  biology.  In 
Figures  19  and  20  are  represented  not  only  the  various  nu- 
trients found  in  some  of  our  most  common  fcods,  but  also 
their  relative  proportions  in  percentages. 

52.  Composition  of  various  foods.  —  (Home  study.) 

1.  Name  the  foods  represented  in  Figures  19  and  20  that  are 

derived  from    animals;    name    those    obtained    from 
plants. 

2.  Which  of  the  two  classes  of  foods,  named  in  1  above,  has 

on  the  average  the  larger  percentage  of  protein? 

3.  In  which  of  these  two  classes  do  you  find  the  larger 

amount  of  fats  ? 

4.  Which  class  has  the  larger  percentage  of  carbohydrates? 

5.  What,  then,  are  the  principal  differences  in  the  composi- 

tion of  animal  and  vegetable  foods? 

6.  Name  the  various  food  substances  found  in  one  animal 

food  and  in  one  vegetable  food,  giving  in  each  case  the 
percentage  of  each  nutrient. 

IV.   USES  OF  THE  FOOD  SUBSTANCES 

53.  Uses  of  the  food  substances  to  plants  and  animals.  — 
In  our  study  of  green  plants  we  learned  that  these  living 
organisms  can  manufacture  the  food  substances  they  need 
from  the    simple    compounds   (water,   carbon    dioxid,   and 
mineral  matters)  found  in  earth,  air,  and  water,  and  that 
these  food  substances  are  used  for  the  making  of  protoplasm 
and  the  liberation  of  energy.     Animals  and  human  beings, 
on  the  other  hand,  since  they  cannot  make  their  foods,  are 


FOODS  AND  THEIR    USES  51 

either  directly  or  indirectly  dependent  on  plants  for  their 
food  supply.  They  use  these  food  materials,  however,  for 
the  same  purposes  as  do  plants.  The  use  of  the  individual 
food  substances  will  now  be  considered. 

54.  Uses  of  proteins.  —  Protein  is   an  essential  constit- 
uent of  plant  protoplasm  (P.  B.,  43).     This  class  of  nutrients 
is  also  essential  for  the  growth  and  repair  of  the  living  sub- 
stance in  muscle,  nerve,  and  all  other  tissues  of  the  human 
body.     Proteins  may  also  be  oxidized  in  the  body  and  give 
heat  and  muscular  energy. 

55.  Uses  of  fats  and  carbohydrates. — The  chief  fuel  in- 
gredients of  food,  however,  are  the  fats  and  carbohydrates. 
Most  of  the  fat  in  our  foods  is  probably  oxidized  soon  after 
it  reaches  the  cells  to  furnish  heat  and  power,  and  this  class 
of  nutrients  possesses  two  and  a  half  times  the  fuel  value  of 
any  other  kind  of  food  substance.     This  is  the  reason  why 
the  inhabitants  of  arctic  countries  eat  such  large  quantities 
of  fatty  foods. 

The  starches  and  sugars  of  bread,  potato,  fruits,  and  milk 
are  also  used  as  fuel.  The  fat  which  we  stated  (44)  is 
stored  in  various  parts  of  the  body,  is  derived  partly  from  the 
carbohydrates  and  partly  from  the  fats  in  our  food,  and  this 
acts  as  a  reserve  fuel.  That  portion  of  the  fat  which  is  stored 
in  the  deeper  layers  of  the  skin  helps  to  keep  our  bodies  warm 
by  preventing  the  escape  of  heat. 

56.  Comparison  of  uses  of  the  nutrients.  —  It  is  evident 
that  the  three  nutrients  thus  far  studied  may  be  used  to  supply 
the  body  with  energy.     If  our  diet  is  deficient  in  any  one  of 
the  three,  the  others  supply  the  need,  and  are  burned  instead. 
For  growth   and   repair,  however,    proteins  are  absolutely 
essential ;  neither  carbohydrates  nor  fat  can  be  transformed 


52  HUMAN  BIOLOGY 

into  this  essential   ingredient  of  protoplasm.      Hence,   an 
animal  soon  dies  if  it  is  not  supplied  with  proteins. 

If  a  machine  is  to  do  a  large  amount  of  work,  it  must  be 
large  enough  and  strong  enough,  and  must  have  plenty  of 
fuel.  This  is  true  of  the  body  machine.  A  man  who  does 
hard  work,  and  a  good  deal  of  it,  needs  plenty  of  proteins 
in  his  food  to  build  up  his  tissues  and  keep  them  in  f epair, 
and  plenty  of  fats  and  carbohydrates  for  fuel. 

57.  Uses  of  mineral  matters   and   water.  —  The  mineral 
matters  like  phosphate  and  carbonate  of  calcium  and  magne- 
sium are  necessary  for  making  bones  and  teeth,  and  for  the 
making  of   protoplasm  (P.  B.,   43).     Salt  is  used   in  large 
quantities   by   all   civilized   nations;    it   makes  food  more 
palatable  and  it  is  important  in  the  making  of   digestive 
fluids. 

Water  is  an  essential  constituent  of  protoplasm,  and  hence 
the  body  needs  it  constantly.  Water  also  aids  in  dissolving 
foods.  A  considerable  amount  is  supplied  by  the  water 
contained  in  some  of  our  solid  foods,  and  we  get  the  rest 
from  the  water  and  other  beverages  that  we  drink. 

V.   COOKING  OF  FOODS 

58.  Importance   of  proper  cooking.  —  Some  of  our  foods,  like 
milk,  nuts,  and  fruits,  are  eaten  without  being  cooked.     The  great 
majority,  however,  before  they  are  taken  into  our  bodies  are  changed 
considerably.     It  is  important  for  us  to  learn  the  essential  prin- 
ciples of  good  cooking,  since  food,  as  often  prepared,  loses  much  of 
its  flavor,  becomes  more  or  less  indigestible,  and  is  deprived  of  a 
considerable  percentage  of  its  nutrition. 

59.  Reasons    for    cooking    animal    foods.  —  In    civilized    com- 
munities meats  and  other  animal  foods  are  usually  cooked  by  broil- 
ing, roasting,  boiling,  or  frying.     The  reasons  for  cooking  the  flesh 


FOODS  AND   THEIR   USES  53 

of  animals  are  these :  (1)  proper  cooking  loosens  and  softe'ns  the 
fibers,  thus  preparing  the  meat  for  mastication  and  for  the  action 
of  the  digestive  juices ;  (2)  the  heat  kills  the  harmful  bacteria  and 
other  parasites  (e.g.  tapeworms)  that  are  sometimes  found  in  foods 
of  animal  origin;  (3)  cooking  makes  the  meat  more  attractive  in 
appearance  and  often  improves  its  flavor ;  and  (4)  cooked  meat  is 
more  cynpletely  digested.  It  is  probably  true,  however,  that  raw 
or  partly  cooked  meats  are  more  easily  digested. 

60.  Frying.  —  If  meats  are  fried,  the  skillet  should  be  very  hot, 
so  that  the  surface  of  the  meat  may  be  coagulated  at  once,  thus 
preventing  the  escape  of  nutrients  and  the  entrance  of  fats.     Frying 
usually  involves  the  use  of  additional  fats,  and  since  frying  tends  to 
make  foods  indigestible,  this  is  doubtless  the  poorest  method   of 
cooking  meat. 

61.  Soups.  —  If  we  wish  to  obtain  nutritious  soups,  the  meat 
should  be  cut  into  rather  small  pieces  and  first  put  into  cold  water 
to  which  a  little  salt  has  been  added.     A  small  proportion  of  the 
proteins,  and  large  amounts  of  so-called  " extractives,"  or  flavoring 
matters,  are  drawn  out  by  the  water  and  salt,  and  since  the  meat  is 
in  small  pieces,  a  considerable  proportion  of  the  mineral  matter  is 
thus  dissolved.     When  we  warm  the  mixture,  we  cause  the  fats  to 
melt,  and  when  it  is  boiled,  much  of  the  tough  connective  tissue  is 
made  more  or  less  soluble  by  being  turned  into  gelatin.     The  soups 
thus  obtained  are  made  more  palatable  by  the  addition  of  condi- 
ments. 

The  meat  which  is  left  after  the  soup  has  been  prepared  is  more  or 
less  tasteless.  Only  small  percentages,  however,  of  the  nutrients 
have  been  withdrawn ;  hence  the  soup  meat  should  not  be  thrown 
away,  but  should  be  used  as  described  in  71. 

62.  Stewing.  —  It  is  unfortunate  that  stews  are  not  more  highly 
regarded  in  American  families,  for  by  this  method  of  preparing 
animal  foods  all  the  nutritive  ingredients  are  utilized.   To  make  a  good 
stew  the  meat  should  be  cut  into  rather  small  pieces  and  placed  in 
cold  water.     Some  of  the  flavoring  matters  and  soluble  proteins 


54  HUMAN  BIOLOGY 

pass  out  into  the  broth,  making  it  rich  and  nutritious.  When  the 
stew  is  allowed  to  simmer  for  several  hours  on  the  back  of  the  stove, 
the  meat  itself  becomes  tender  and  readily  digestible.  The  addi- 
tion of  vegetables  makes  it  a  most  nourishing  and  palatable  dish. 

63.  Boiling  meats.  —  When  the  meat  itself  is  to  be  eaten,  and 
the  broth  is  not  to  be  used,  the  whole  piece  should  be  plunged  into 
boiling  water  for  a  few  moments.     In  this  way  the  protein  on  the 
surface  is  quickly  coagulated,  and  the  crust  thus  formed  prevents 
the  loss  of  the  meat  juices.     The  temperature  of  the  water  should 
then  be  reduced  somewhat  below  the  boiling  point  by  pushing  the 
kettle  toward  the  back  of  the  stove,  and  the  meat  should  then  cook 
slowly  until  it  is  done.    A  piece  of  meat,  when  cooked  in  this  way, 
is  tender  and  juicy  throughout.     If,  however,  the  water  is  kept  at 
the  boiling  point  (212°  F.),  the  meat  may  be  easily  torn  apart,  but 
the  fibers  are  found  to  be  hard  and  stringy. 

64.  Roasting  and  broiling.  —  The  best  method  of   cooking  the 
flesh  of  animals,  if  the  broth  is  not  desired,  is  by  roasting  or  by  broil- 
ing, since  smaller  percentages  of  the  nutrients  are  lost  than  is  the 
case  in  boiling.     The  outer  layer  of  protein  must,  however,  be  coagu- 
lated at  once,  and  for  this  purpose  a  very  hot  fire  is  needed. 

When  the  piece  to  be  roasted  is  small,  the  high  temperature 
should  be  maintained  until  the  meat  is  cooked.  A  large  roast,  on 
the  other  hand,  after  the  outer  covering  has  been  coagulated,  requires 
a  slower  fire  and  a  longer  time ;  meat  is  not  a  good  conductor  of 
heat,  and  a  hot  oven  would  scorch  the  outside  before  the  central  mass 
could  become  thoroughly  cooked.  A  better  crust  is  formed  on  the 
outer  surface  of  the  roast  if  the  meat  juices  in  the  pan  (mostly  fat) 
are  frequently  poured  over  the  surface  of  the  roast.  This  is  called 
"basting." 

65.  Reasons  for  cooking  vegetables.  —  The  starches,  which  are 
present  in  large  quantity  in  foods  of  vegetable  origin,  are  usually 
inclosed  in  cells,  the  walls  of  which  are  formed  of  indigestible  cellu- 
lose.    Hence,  before  starch  can  be  digested,  it  must  be  freed  from 
this  cellulose  envelope.    This  is  largely  accomplished  by  cooking, 


FOODS  AND   THEIR    USES  55 

which  causes  the  starch  grains  to  swell.  The  cell  walls  are  broken 
open  in  this  way,  and  when  the  grains  burst,  a  larger  surface  is  ex- 
posed to  the  action  of  the  digestive  juices  (Figure  21).  This  is 
strikingly  shown  in  popping  corn.  The  crust  of  bread  is  more  easily 
digested  than  the  softer  parts,  and  toasting  bread  increases  its  di- 
gestibility, because  this  browned  starch  (sometimes  called  soluble 
starch)  requires  less  change  before  it  can  be  used  by  the  body. 

66.   Boiling  vegetables.  —  Experiments  have  shown  that  a  good 
deal  of  nutriment  is  lost  by  boiling  vegetables  in  water.     Much  of 


FIG.  21.  —  A,  cells  of  raw  potato  with  starch  grains  inclosed  in  the  cellulose 
walls.  B,  cells  of  a  potato  well  steamed  and  mashed ;  starch  grains  have 
been  burst  by  the  heat. 

this  waste  may  be  avoided,  however,  if  one  heeds  the  following 
directions:  (1)  vegetables  should  be  cooked  as  far  as  possible  in  their 
peels,  for  these  outside  coverings  keep  the  sugar,  proteins,  and  min- 
eral matters  from  being  drawn  out  by  the  water ;  (2)  if  the  vege- 
tables must  be  peeled  and  cut  up,  the  pieces  should  be  relatively  large, 
as  a  smaller  surface  is  thus  exposed  to  the  water ;  (3)  the  amount  of 
water  should  be  as  small  as  possible,  and  the  vegetables  should  be 
cooked  rapidly,  in  order  to  give  less  time  for  the  solvent  action  to 
take  place. 

67.  Bread  making. — When  bread  is  made,  water  (or  milk), 
butter,  salt,  sugar,  and  yeast  are  added  to  flour.  After  the  mixture 
has  been  stirred  together,  a  sticky  mass  of  dough  is  formed,  which,  in 


56  HUMAN  BIOLOGY 

a  warm  place,  begins  to  rise.  This  is  due  to  the  fact  that  the  yeast 
cells  change  the  sugar  into  alcohol  and  carbon  dioxid.  Bubbles  of 
gas  are  thus  imprisoned  in  the  sticky  dough.  While  expanding  and 
seeking  to  escape,  the  gas  makes  the  solid  mass  porous.  After  the 
bread  has  risen  sufficiently,  it  is  kneaded  in  order  to  break  up 
the  large  bubbles  and  in  order  to  distribute  the  gas  throughout 
the  dough.  When  the  bread  is  baked,  the  alcohol  and  carbon 
dioxid  pass  off  into  the  air,  leaving  the  bread  light  and  digestible. 

VI.   FOOD  ECONOMY 

68.  Importance    of   food    economy.  —  It   is  said  that  in 
a  large  proportion  of  American  families  more  than  half  the 
total  income  is  spent  for  food,  and  that  the  remainder  of 
the  income  must  serve  for  rent,  fuel,  clothing,  doctor's  bills, 
and  other  expenses.     Hence,  any  saving  that  can  be  made 
in  the  annual  food  bill  of  a  family  should  result  in  a  surplus 
which  may  well  serve  as  a  nucleus  of  a  saving's  bank  account, 
or  may  be  used  in  improving  the  home  surroundings  or  in  se- 
curing wider  means  of  education  and  enjoyment.    The  average 
American,  however,  is  far  from  economical  in  the  matter 
of  foods.     In  the  first  place  there  is  often  extravagance  in 
the  purchase  of  food,  and  in  the  second  place  foods  are  fre- 
quently wasted  in  the  home. 

69.  Comparative  cost   of   foods.  —  (Home   study.)     The 
chart  shown  in  Figure  22  exhibits  (1)  the  cost  price  of  each  of 
the  foods  represented,  (2)  the  weight  of  the  food  that  may  be 
purchased  for  25  cents,  and  (3)  the  weight  of  the  solid  food 
substances  (except  mineral  matters)  that  may  be  purchased 
in  each  food  for  25  cents.     Note  at  the  top  of  the  chart  the 
short  vertical  lines  that  indicate  1  pound,  2  pounds,  etc.,  of 
solid  nutrients;   hence,  if  25  cents  is  spent  for  wheat  flour, 
about  f  of  a  pound  of  protein  can  be  secured,  J  of  a  pound 
of  fat,  and  about  6J  pounds  of  carbohydrates. 


FOODS  AND   THEIR    USES 


57 


CARBOHYDRATES 


r      i 


THE  HEAVY  BLACK  LINES  IN  THE  CHART  BE- 
LOW INDICATE  THE  RELATIVE  FUEL  VALUE 
IN  ONE  POUND  OF  EACH  OF  THE  NUTRIENTS 


/      BEEF,  SIRLOIN 

O 

§1 

h 

FOOD  MATE- 
RIALS FOR 
25  CENTS. 

WEIGHTS  OP  NUTRIENTS  AND  FUEL  VALUE 
IN  25  CENTS'  WORTH. 

CTS 

LB*. 

1  LB.                                    3  LBS.                                    5  L 

25.  C 

1             L        1        _l 

1.00 

il 

MB 

BEEF,  ROUND 

BEEF,  NECK 

16.0 

6.0 

1.67  pBPil      

mpm      i  1= 

MUTTON,  LEG 

22.  C 

1.14  IjjjjLjjj^^j  

HAM,  SMOKED 

15.0 

,.»N^    1 

SALT  PORK  ,  VERY  FAT 

12.0 

2.08 

| 

CODFISH,  FRESH 
CODFISH,  SALT 

s.o 

7.0 

3.13 
3.57 

•                                                                                                              

MACKEREL,  SALT 

12.0 

2.08 

[       1 

•••••••• 

OY8TER8,  35  CTS.  QUART 

18.0 

1.43 

| 

• 

EGGS,  25  CENTS  DOZEN 

14.7 

1.70 

£js— 

MILK,7  CENTS  QUART 

3.E 

7.14 

38    i  ',! 

CHEESE,  WHOLE  MILK 

15.0 

1.67 

•H^r     j 

CHEESE,  SKIM  MILK 

8.0 

3.13 

,  ':.:>:     \'//\ 

•••••••••••1 

BUTTER 

30.  C 

0.83 

| 

••••••••^M 

SUGAR 

5.0 

5.00 

WHEAT  FLOUR 

3.0 

8.33 

ID                            .         :.    ,  .... 

'  ! 

MMMHK    ^S 

WHEAT  BREAD 

7.0 

3.57 

M   I  J           ....                

CORN  MEAL 

2.5 

10.00 

,  

1  

BEANS 

5.0 

5  00 

lour                   :    i 

POTATOES 

1.2 

STANDARD  FOR   DAILY  DIET  FOR 
MAN  AT   MODERATE  WORK 
V 

b$f  f            i 

AMERICAN 

—.^m—m^m 

FIG.  22.  —  Economy  in  the  purchase  of  foods.  Prices  in  this  chart  were  those 
in  the  year  1900.  Compare  with  prices  to-day.  (U.  S.  Department  of 
Agriculture.) 


58  HUMAN  BIOLOGY 

1.  Name  the  foods  represented  in  Figure  22  that  are  derived 

from  animals ;  name  those  obtained  from  plants. 

2.  On  the  average,  can  larger  amounts  of  the  animal  or  of 

the  vegetable  foods  represented  on  the  chart  be  pur- 
chased for  25  cents  ? 

3.  Bearing  in  mind  the  relative  work  and  expense  in  pro- 

ducing animal  and  vegetable  foods  suggest  some 
explanations  for  the  answer  you  have  given  to  ques- 
tion 2. 

4.  Which  one  of  the  foods  on  the  chart  would  you  buy  if 

you  wished  to  get  the  largest  amount  of  solid  nutri- 
tion for  25  cents;  that  is,  which  food  is  the  most 
economical  ? 

5.  From  which  kind  of  food  would  you  get  the  smallest 

amount  of  solid  nutrients?  Name  other  foods  on 
the  chart  which  are  more  expensive  per  pound  than 
the  one  that  you  have  just  named. 

6.  Which  of  the  three  kinds  of  beef  named  on  the  chart 

would  be  the  most  economical  for  soup  or  stew? 

7.  Name  three  classes  of  food  substances  needed  in  the  diet 

of  the  average  American  engaged  in  moderate  work 
(see  last  line  on  the  chart),  and  estimate  the  weight 
of  each  that  is  needed  during  a  day. 

8.  Which  food  on  the  chart  comes  the  nearest  to  supplying 

in  the  right  proportions  all  the  nutrients  named  in  7  ? 
In  the  food  you  have  named  which  kind  of  food  sub- 
stance is  not  present  in  sufficient  proportion  ? 

9.  Why  is  it  better  to  eat  a  variety  of  foods  rather  than 

any  one  kind? 

10.   Suggest  a  reason  why  meat  and  potato  should  be  eaten 
together ;  bread  and  butter. 

70.  Economy  in  the  purchase  of  foods.  —  The  animal 
foods,  we  have  just  learned,  are  considerably  more  expensive 
than  the  staple  foods  of  vegetable  origin.  Hence,  in  an 
economical  household  the  proteins  needed  by  the  body 
should  be  largely  obtained  from  vegetable  foods  like  bread, 
corn  meal,  and  beans.  If  this  plan  were  followed,  a  con- 


FOODS  AND   THEIR   USES  59 

siderable  saving  in  the  year's  expenses  might  be  effected. 
Figure  22  shows  the  weights  of  different  food  materials  that 
may  be  purchased  for  25  cents.  On  comparing  the  two 
meats  at  the  top  of  the  chart,  one  can  see  that  a  greater 
fraction  of  a  pound  of  solid  nutriment  may  be  obtained  by 
spending  25  cents  for  round  steak  than  could  be  secured  by 
the  purchase  of  sirloin.  •  Yet  the  latter  is  bought  even  in 
very  poor  families.  From  oysters  one  gets  less  of  the  solid 
nutrients  than  from  any  other  food  represented  on  the 
chart;  therefore,  if  one's  income  is  small,  this  land  of  food 
should  be  regarded  as  a  luxury,  seldom  purchased  except 
in  case  of  sickness. 

71.  Economy  in  the  use  of  foods.  —  In  discussing  the 
cooking  of  foods,  we  suggested  some  of  the  ways  by  which 
the  loss  of  nutritive  ingredients  may  be  prevented.  We  waste 
foods,  however,  in  other  ways ;  for  instance,  we  often  throw 
away  bones  and  gristle,  regardless  of  the  fact  that  they  con- 
tain a  considerable  percentage  of  protein,  gelatin,  and  fat 
from  which  one  might  make  a  nutritious  soup.  It  has  been 
found  that  large  proportions  of  the  food  materials  still  remain 
in  a  piece  of  meat  after  it  has  been  used  for  soup,  even  though 
it  is  more  or  less  tasteless.  This  meat  should  not  be  thrown 
away,  however,  but  should  be  chopped  up  and  combined 
with  vegetables  and  condiments  to  make  a  hash.  The 
garbage  pails  of  most  kitchens  receive  far  too  large  a  per- 
centage of  the  food  that  is  bought  for  the  household,  and 
many  a  dollar  could  be  saved  for  other  purposes  if  more 
care  were  exercised  to  prevent  this  waste. 

The  food  problem,  then,  for  the  healthy  human  being  is 
this  —  how  to  obtain  the  largest  amount  of  good,  nutritious  food 
for  the  least  money.  To  this  problem  an  intelligent  house- 
keeper, if  she  can  be  led  to  see  the  importance  of  the  subject, 


60  HUMAN  BIOLOGY 

will  devote  considerable  thought.  This  problem  cannot 
be  solved,  as  we  have  seen,  by  consulting  market  prices 
only,  for  often  the  highest-priced  foods  contain  small  per- 
centages of  the  nutrients.  Neither  can  we  be  sure  of  a  good 
supply  of  foods  by  following  our  tastes.  To  many  people 
cakes  and  sweetmeats  are  more  appetizing  than  sandwiches 
and  cereals.  Yet  it  is  the  latter  that  usually  supply  the 
available  proteins,  at  a  lower  cost. 

The  composition  of  various  foods  can  be  found  only  by 
chemical  analysis,  and  their  nutritive  value  can  be  deter- 
mined only  by  experiment.  Fortunately  these  analyses 
and  experiments  are  being  carried  on  by  the  United  States 
government.  The  results  are  published  in  the  Bulletins  l 
of  the  Department  of  Agriculture,  Washington,  D.C.,  many 
of  which  will  be  sent  free  to  any  address. 

VII.   DAILY  DIET 

72.  Amount  of  each  nutrient  required.  —  Many  in- 
vestigations have  been  carried  on,  in  this  country  and  in 
Europe,  to  determine  the  amount  of  each  kind  of  nutrient 
needed  per  day  for  the  work  of  the  body.  The  conclusions 
that  were  drawn  from  this  study  are  represented  on  the  last 
line  of  Fig.  22.  According  to  these  conclusions  the  average 
American,  when  doing  moderate  work,  requires  about  one 
fourth  of  a  pound, of  proteins  to  provide  for  the  growth  and 
repair  of  the  body,  and  a  quarter  of  a  pound  of  fat  and  a 
pound  of  carbohydrates  to  furnish  the  needed  energy.2  This 

1  The  most  suggestive  of   these  publications   are  **  Foods,  and 
the  Principles  of  Nutrition,"   "Meats:  Composition  and  Cook- 
ing";   "Milk  as  a  Food";   "Fish  as  a  Food";  "Sugar  as  a 
Food." 

2  Recently,  however,  at  the  Scientific  School  of  Yale  University, 
some  very  careful  experiments  have  been  performed  by  Professor 
Chittenden  which  seem  to  prove  that  this  quarter  of  a  pound  of  pro- 


FOODS  AND   THEIR   USES  61 

is  about  the  amount  eaten  by  a  man  of  average  appetite. 
In  order  to  secure  a  heathful  diet,  the  general  principles 
stated  in  the  following  paragraphs  should  be  borne  in  mind, 
by  an  adult  or  by  a  growing  boy  or  girl. 

73.  Necessity  for  a  mixed  diet.  —  A  sufficient  variety 
of  foods  should  be  eaten  at  each  meal  to  obtain  all  the 
nutrients  needed.  In  69  we  learned  that  in  none  of  the 
foods  on  the  chart  are  the  nutrients  in  the  right  proportions. 
Cow's  milk  comes  the  nearest  to  being  a  perfect  food,  but 
its  percentage  of  carbohydrates  is  too  small.  If  we  were 
to  feed  on  meat  alone,  we  should  get  too  large  an  amount  of 
proteins;  while  most  of  the  vegetable  foods  are  lacking  in 
fats.  Hence,  a  well-balanced  diet  should  consist  of  a  mixture 
of  many  kinds  of  foods.  Such  a  diet  will  supply  not  only 
the  proteins,  fats,  and  carbohydrates,  but  also  the  mineral 
matters  so  necessary  in  the  development  of  the  bones  and 
teeth,  and  in  the  making  of  living  substance.  In  fact,  some 
foods,  such  as  spinach,  are  valuable  chiefly  on  account  of 
the  mineral  matters  which  they  contain.  If  the  appetite 
is  normal,  one  is  fairly  sure  to  secure  the  nutrients  in  ap- 
proximately the  right  proportions.1 

tein  for  each  day  is  considerably  more  than  the  body  really  needs. 
Dr.  Chittenden  experimented  on  five  of  the  Yale  University  pro- 
fessors, on  thirteen  soldiers  of  the  United  States  army,  and  on  five 
of  the  best  athletes  at  Yale ;  he  found  that  all  agreed  that  they 
could  do  better  physical  and  mental  work,  and  do  it  without  any  loss 
of  weight,  when  they  had  become  accustomed  to  taking  less  than  half 
their  ordinary  amount  of  proteins.  In  several  instances  rheuma- 
tism, biliousness,  and  other  derangements  of  the  body  were  cured  by 
this  restricted  diet.  "There  is  no  question,  in  view  of  our  results," 
says  Professor  Chittenden,  "  that  people  ordinarily  consume  much 
more  protein  food  than  there  is  any  real  physiological  necessity  for, 
and  it  is  more  than  probable  that  this  excess  of  food  is  in  the  long 
run  detrimental  to  health,  weakening  rather  than  strengthening  the 
body,  and  defeating  the  very  objects  aimed  at." 

1  It  is  desirable  that  pupils  prepare  a  list  of  the  kinds  of  foods  and 
beverages,  stating  quantity  of  each,  that  formed  their  diet  on  the 


62 


HUMAN  BIOLOGY 


74.  Avoidance   of    indigestible    foods.  —  Frequently   in- 
dividuals find  that  they  cannot  eat  certain  kinds  of  foods, 
e.g.  cheese,  honey,  cucumbers,  without  discomfort.     Hence, 
in  selecting  their  diet  these  foods  should  not,  of  course,  be 
eaten.     Foods  that  are  hard  to  digest,  such  as  fried  foods, 
heavy  bread,  or  pastry,  should  be  avoided,  especially  by 
growing  girls  and  boys. 

75.  Sugars  as  a  part  of   the  diet.  —  Carbohydrates,  we 
have   found,   are   essential   constituents   of   our  foods.     If, 
however,  sugars  are  eaten  between  meals,  too  much  of  this 
kind  of  food  substance  is  likely  to  be  consumed,  the  appetite 
for  other  foods  is  lessened,  and  digestive  disturbances  are 
likely  to  follow.     Consequently  the  pastry  and  confectionery 
that  are  eaten  should  form  a  part  of  dessert,   j 


76.    Review  of  Foods 


NAME  OF 
NUTRIENT 

TEST  POK 
NUTRIENT 

USES  OF 
NUTRIENT 

FOODS  CONTAINING 
NUTRIENT 

Protein 

Coagulates 

Necessary  for 

Meat,  eggs, 

(albumin, 

when 

the  manu- 

milk, cheese 

nitrogenous 

heated. 

facture  of 

(among  ani- 

food). 

Turned  to 

protoplasm. 

mal  foods), 

yellow 

When  oxidized 

and  beans, 

color  by 

releases 

peas,  oat- 

nitric 

energy. 

meal  (among 

acid. 

vegetable 

foods). 

three  meals  of  some  stated  day.  These  menus  should  then  be  read 
and  discussed  by  teacher  and  pupils,  and  such  suggestions  for  im- 
provement should  be  made  as  may  seem  necessary. 


FOODS  AND   THEIR    USES 


NAME  OF 

TEST  FOR 

USES  OF 

FOODS  CONTAINING 

NUTRIENT 

NUTRIENT 

NUTRIENT 

NUTRIENT 

Starch. 

Turned  to  a 

Changed  to 

Vegetable 

blue  color 

sugar,  source 

foods 

by  iodine 

of  energy, 

(especially 

solution. 

and  may  be 

cereals)  . 

transformed 

-  » 

into  body 

fat. 

Sugar. 

Fehling's 

Source  of 

Vegetable 

solution  is 

energy. 

foods 

turned 

Transformed 

(especially 

orange  or 

into  body 

fruits)  ;  milk 

red  when 

fat. 

sugar  is 

boiled  with 

found  in 

grape 

milk. 

sugar. 

Fats  (or 

Make  trans- 

Source of 

Animal  foods 

oils). 

lucent 

energy. 

(especially 

spots  on 

Transformed 

butter,  pork, 

paper. 

into  body 

cheese), 

Dissolved 

fat. 

vegetable 

•'  , 

by  ether  or 

foods,  as 

benzine. 

nuts,  cocoa, 

chocolate. 

Mineral 

Left  as  ash 

Help  to  form 

Common  salt  ; 

matters. 

after  food 

bone,  teeth, 

mineral 

is  burned. 

and  other 

matters  in 

tissues. 

most  vege- 

Aid in 

table  and 

digestion. 

animal  foods. 

CHAPTER  IV 

STIMULANTS   AND   NARCOTICS 
I.  DEFINITIONS 

77.  Stimulants.  —  In  the  preceding  chapter  we  discussed 
food  substances,  and  these,  we  learned,  yield  material  for  the 
repair  or  growth  of  the  body,  or  supply  the  fuel  necessary 
for  producing  energy  in  the  body.     But  in  addition  to  the 
various  nutrients  that  may  be  used  for  one  or  all  of  these 
purposes,  we  often  take  with  our  food  certain  substances 
that  are  not  useful  to  any  considerable  extent  in  any  of  these 
ways.     As  examples  of  such  substances,  we  may  mention 
spices.     Such   substances   add   an  agreeable   flavor  to   our 
foods,  and  so  stimulate  our  appetites ;  hence,  they  are  known 
as  stimulants.     A-  stimulant  is  any  agent*  that  temporarily 
quickens  some  process  in  the  body.     The  most  common  stimu- 
lants are  tea,  coffee,  and  alcohol. 

78.  Narcotics.  —  Another    class    of   substances    that   we 
sometimes  use  has  an  effect  directly  opposite  to  that  of 
stimulants.     Ether,  morphine,  and  chloroform,  for  example, 
do  not  quicken  any  process  in  the  body  as  do  stimulants, 
but,  on  the  contrary,  lessen  the  degree  of  activity.     Any 
compound  that  acts  in  this  way  is  called  a  narcotic.     A 
narcotic  is  any  substance  that  directly  induces  sleep,  blunts 
the  senses,  and  in  sufficient  amounts  produces  complete  in- 
sensibility. 

64 


STIMULANTS  AND  NARCOTICS  65 

II.  BEVERAGES 

79.  General  effect  of  tea  and  coffee  on  the  body.  —  The 
effect  of  tea  and  coffee  on  the  body  is  due  to  the  presence  of 
essentially  the  same  stimulant  in  both  (caffein),  which  acts 
largely  on  the  nervous  system.     In  both  tea  and  coffee,  as 
they  are  usually  prepared,  is  another  substance  known  as 
tannin.     This  chemical,  when  obtained  from  the  bark  of 
certain  trees,  is  used  in  tanning  or  hardening  leather.     When 
tannin  is  taken  into  the  stomach,  it  is  found  to  injure  the 
mucous  membrane  and  to  retard  digestion. 

80.  The  preparation  of  tea  and  coffee.  —  To  prepare  tea 
properly,  boiling  water  should  be  poured  upon  tea  leaves, 
and  the  infusion  allowed  to  stand  only  a  few  minutes  before 
pouring.     Tea  should  never  be  put  on  the  stove  to  boil, 
for  two  reasons :    in  the  first  place,  by  this  treatment  the 
delicate  taste  and  odor  of  the  beverage  are  lost ;  and  in  the 
second  place,  if  the  tea  infusion  is  boiled,  a  considerable 
quantity  of  the  tannin  is  dissolved  by  the  water.     Obviously 
the  tea  grounds  should  not  be  used  a  second  time. 

Most  that  has*  been  said  in  regard  to  tea  applies  equally 
well  to  coffee,  except  that  in  the  preparation  of  coffee  the  in- 
fusion should  be  put  on  the  stove  and  allowed  to  come  to  a 
boil ;  it  should  then  be  poured  out,  and  should  not  stand  on 
the  coffee  grounds ;  otherwise  the  tannin  will  be  extracted. 
Coffee  is  best  prepared  by  the  use  of  a  percolator,  since  in 
this  utensil  the  water  is  continuously  forced  over  the  ground 
coffee. 

81.  The   use   and   abuse   of    tea   and    coffee.  — "  When 
properly  made,  tea  in  moderation  is  a  wholesome,  agreeable, 
and   refreshing    stimulant    beverage,    particularly    grateful 
in  conditions   of  mental   or  physical   weariness.     Used  hi 


66  HUMAN  BIOLOGY 

excess,  it  exerts  a  harmful  influence  upon  the  nervous  sys- 
tem, and  in  a  too  strong  form  injures  the  digestive  organs." 
The  foregoing  remarks,  quoted  from  Harrington's  "  Practi- 
cal Hygiene/'  apply  to  adults  rather  than  to  growing  chil- 
dren and  youths;  for  in  early  life  stimulants  of  every  kind 
should  be  avoided  as  much  as  possible,  as  they  tend  to 
interfere  with  the  healthful  development  of  the  body.  We 
should  remember  that  tea  and  coffee  are  not  foods,  and  so 
cannot  be  of  use  in  repair  or  growth  of  tissue,  both  of  which 
functions  are  of  prime  importance  during  the  first  twenty 
years  of  life.  The  habitual  use  of  these  beverages,  especially 
at  breakfast,  is  also  likely  to  decrease  the  desire  for  the 
food  that  is  needed. 

82.  Chocolate,  cocoa,  and  soda  water.  —  While  it  is  true 
that  cocoa  and  chocolate  both  contain  a  considerable  amount 
of  nutriment  when  eaten  in  solid  form,  when  prepared  as  a 
beverage,  the  small  amount  so  used  makes  its  food  value 
relatively  unimportant  unless  milk  is  used.     Chocolate  and 
cocoa  contain  a  certain  amount  of  a  stimulant  similar  to 
that  found  in  tea  and  coffee.     Since  the  sirups  and  ice  cream 
used  in  the  preparation  of  soda  water  contain  a  considerable 
amount  of  sugar,  these  drinks  should  not  be  taken  habit- 
ually between  meals,  because  they  tend  to  impair  digestion 
and  to  lessen  the  appetite  at  meal  time  (75). 

83.  Alcoholic  beverages.  —  "  In  the  case  of  an  alcoholic 
beverage  we  have  to  deal  with  something  which,  like  tea 
and  coffee  and  cocoa  and  'temperance  drinks'  is  used  as  a 
beverage,  and  to  that  extent  must  be  classed  in  the  same 
group.     Alcoholic  drinks  are,  however,  taken  as  stimulants, 
and  so  resemble  tea  and  coffee  and  cocoa;  but  they  differ 
from  all  these  in  their  action  upon  the  body.     Moreover, 
their  abuse  gives  rise  not  only  to  degraded  moral  and  social 


STIMULANTS  AND  NARCOTICS  67 

conditions,  but  is  also  attended  with  bad  hygienic  effects. 
Every  one  should  be  informed  of  their  nature  and  of  the 
dangers  attending  their  use."  —  HOUGH  and  SEDGWICK,  "  The 
Human  Mechanism." 

84.  Alcohol  as  a  possible  food.  —  Like  the  carbohydrates 
and  fat,    alcohol   is   composed   of   carbon,    hydrogen,    and 
oxygen.     Since  it  contains  no  nitrogen,  it  has  no  value  in 
the  processes  of  growth  and  repair;  in  other  words,  it  can- 
not be  made  into  protoplasm.     It  cannot,  therefore,  like 
meat,  milk,  and  eggs  answer  as  a  complete  food. 

Alcohol  we  know  may  be  burned  in  lamps  for  the  produc- 
tion of  heat,  and  in  engines  for  the  generation  of  power. 
Professor  Atwater  has  shown  that  alcohol  also,  if  used  in 
sufficiently  small  amounts,  may  produce  within  the  human 
body  a  certain  amount  of  heat  and  muscular  power.  Indeed, 
in  some  cases  of  extreme  weakness,  especially  in  diseases, 
alcohol  is  regarded  by  some  eminent  physicians  as  necessary 
for  saving  life,  though  even  for  this  purpose  it  is  now  being 
used  to  a  less  extent  in  medical  practice. 

85.  Alcohol  as  a  stimulant  and  a  narcotic.  —  On  account 
of  the  amount  imbibed,  however,  alcohol,  as  ordinarily  used 
in  beverages,  is  practically  always  either  a  stimulant  or  a 
narcotic.     In  later  sections  we  shall  discuss  the  effects  of 
alcohol  on  various  organs  of  the  body.     One  fact  should,  how- 
ever, be  continually  emphasized;  namely,  that  even  if  it 
should  be  taken  for  granted  that  alcohol,  when  used   by 
adults  in  moderation,  may  generate  a  certain  amount  of  energy, 
still  this  is  an  exceedingly  dangerous  compound  to  introduce 
in  any  form  into  the  diet  of  a  boy  or  girl.     In  the  first  place, 
it  interferes  with  the  healthy  growth  of  protoplasm;  and 
in  the  second  place,  the  use  of  liquors  in  moderation  by  a 
great  many  people,  both  young  and  old,  is  absolutely  im- 


68  HUMAN  BIOLOGY 

possible.  Men  never  become  drunkards,  paupers,  and  crim- 
inals by  taking  the  nutrients,  starch,  sugar,  fat,  or  protein, 
nor  does  the  taste  for  any  one  kind  of  food  become  uncontrol- 
lable, as  is  so  often  the  case  with  alcohol.  "  Till  he  has  tried 
it,  no  one  can  be  sure  whether  he  can  control  his  appetite 
or  not.  When  he  has  ascertained  the  fact,  it  is  often  too 
late.  The  child  should  be  taught  to  avoid  alcohol  because 
it  is  dangerous  to  him.  The  only  certain  safety  for  the  young 
lies  in  total  abstinence. " 

86.  Effects  of   small   and  large  quantities  of  alcohol.  — • 

The  effects  of  alcohol  on  the  body  depend  very  largely  upon 
the  quantity  taken;  if  the  amount  is  small,  alcohol  may 
possibly  be  regarded  as  a  source  of  energy,  and  hence  in  a 
limited  sense,  as  a  food ;  in  larger  amounts  it  increases  tem- 
porarily the  activity  of  the  organs  of  the  body,  and  so  it 
seems  to  become  a  stimulant;  if  still  larger  quantities  are 
taken,  the  narcotic  effects  of  alcohol  are  shown  in  complete 
insensibility;  and  finally,  a  sufficient  amount  may  be  con- 
sumed to  poison  the  organs  and  cause  death.  No  one  who 
begins  the  use  of  alcohol  expects  to  take  such  an  amount  that 
it  will  act  as  a  poison,  or  even  like  a  narcotic.  There  is, 
however,  a  constant  danger  that  he  will  do  so. 

87.  Professor  Hodge's  experiments  with  dogs.  —  During 
the  years  1895  to  1900,  Professor  Hodge  of  Clark  Univer- 
sity,  Worcester,   Mass.,   carried  on  some  very  instructive 
experiments  upon  dogs.     He  secured  four   spaniel  puppies 
(Fig.  23),  all  of  which  were  born  on  Washington's  Birthday, 
1895 ;  the  two  males  were  brothers,  and  the  females  sisters. 
Professor  Hodge  carefully  watched  the  four  for  nearly  two 
months  before  beginning  his  experiments,  in  order  to  pick 
out  the  two  most  vigorous  animals ;  these  he  named  "  Tipsy  " 
and  "  Bum,"  and  then  put  in  with  their  chief  meal  each  day 


STIMULANTS  AND  NARCOTICS  69 

a  moderate  amount  of  alcohol ;  it  was  not  enough,  however, 
to  cause  any  evidence  of  intoxication.  The  other  two 
spaniels,  "  Nig  "  and  "  Topsy,"  received  no  alcohol. 

88.    Effect  of  a  moderate  amount  of  alcohol  on  activity.  — 
For  over  five  years  these  dogs  were  studied,  and  important 


Bum  Tipsy  Nig  Topsy 


FIG.  23. — The  appearance  of  the  four  spaniels  six  months  after  the  experi- 
ments were  begun.  ("  Physiological  Aspects  of  the  Liquor  Problem,"  by 
permission  of  Dr.  Hodge  and  of  Houghton,  Mifflin  &  Co.) 

facts  were  learned  as  to  the  general  effect  of  alcohol  on 
physiological  processes.  Early  in  his  observations  it  became 
evident  to  Professor  Hodge  that  the  dogs  that  were  receiving 
the  alcohol  were  far  less  playful  than  were  those  that  had  no 
alcohol  in  their  food.  To  measure  the  comparative  activity 
of  the  different  animals,  he  attached  to  the  collar  of  each  dog 
a  Waterbury  watch  adjusted  in  such  a  way  that  it  would  tick 


70  HUMAN  BIOLOGY 

once  each  time  the  animal  moved,  and  so  at  the  close  of  each 
day  he  could  determine  and  set  down  the  record  made  by 
each  dog.  He  found  that  for  a  period  of  two  months  and 
more  "  Bum  "  was  only  71  per  cent  as  active  as  "  Nig/'  while 
"  Tipsy"  was  only  57  per  cent  as  active  as  "Topsy  "  ;  in  other 
words,  the  two  alcoholic  dogs  lost  25  per  cent  to  50  per  cent 
of  their  activity. 

89.  Effect  of  a  moderate  amount  of  alcohol  on  skill  and 
endurance.  —  A  second  series  of  experiments  was  made  to 
determine  the  comparative  endurance  of  the  four  dogs  and 
their  ability  to  accomplish  things.     The  animals  were  all 
taught  to  retrieve  a  rubber  ball  when  it  was  thrown  the 
length  of  the  gymnasium  floor,  a  distance  of  100  feet.     At 
each  trial  the  ball  was  thrown  100  times,  and  a  record  was 
kept  of  all  the  dogs  that  started  for  the  ball  and  of  the  one 
that  succeeded  in  bringing  it  back.     When  he  had  averaged 
a  long  series  of  experiments,  Dr.  Hodge  found  that  "  Bum  " 
and  "  Tipsy  "  secured  the  ball  only  about  half  as  often  as  did 
"Nig"  and  "Topsy";   the  two  alcoholic  dogs  also   gave 
evidence  of  much  greater  fatigue  during  the  trials. 

90.  Effect  of  a  moderate  amount  of  alcohol  in  producing 
nervousness.  —  "A  very  striking   result   of  the  entire  re- 
search," says  Dr.  Hodge,  "  and  one  entirely  unexpected  on 
account  of  the  small  doses  of  alcohol  given,  has  been  the  ex- 
treme timidity  of  the  alcoholic  dogs.   .  .  .     While  able  to 
hold  their  own  with  the  other  dogs  in  the  kennel,  the  least 
thing  out  of  the  ordinary  caused  practically  all  the  alcoholic 
dogs  to  exhibit  fear,  while  the  others  evinced  only  curiosity 
or  interest.     Whistles  and  bells,  in  the  distance,  never  ceased 
to  throw  them  into  a  panic  in  which  they  howled  and  yelped, 
while  the  normal  dogs  simply  barked.     This  holds  true  of  all 
the  dogs  that  had  alcohol  in  any  amount." 


STIMULANTS  AND  NARCOTICS  71 

91.  Effect   of  a  moderate   amount  of  alcohol  on  the  off- 
spring. —  Another  most  striking  result  of  the  use  of  alcohol 
was  shown  in  its  effects  on  the  young  of  "  Bum  "  and  "  Tipsy." 
Of  the  twenty-three  puppies  descended  from  these  alcoholic 
animals,  only  17  per  cent  lived  to  be  normal  dogs ;  the  rest 
were  either  deformed,  or  unable  to  nourish  themselves,  and  all 
died  soon  after  birth.     On  the  other  hand,  of  the  forty-five 
young  of  "  Nig  "  and  "  Topsy,"  over  90  per  cent  were  healthy 
puppies.     Hence,  the  puppies  of  the  dogs  that  took  alcohol 
even  in  moderation  were  over  five  times  as  likely  to  die  young 
as  were  the  puppies  born  of  abstaining  parents. 

92.  Effect  of  a  moderate  amount  of  alcohol  on  resistance 
to  disease.  —  In  the  spring  of  1897,  in  the  course  of  these 
experiments,  a  great   many  dogs  throughout  the   city  of 
Worcester  were  afflicted  with  distemper,  and  dogs  sick  with 
the  disease  were  not  uncommon  on  the  streets.     At  that  time, 
Dr.  Hodge  had,  in  all,  five  dogs  that  were  taking  alcohol  and 
four  that  were  not.     It  was  found  that  there  was  a  marked 
difference  in  the  effect  of  the  disease  on  the  two  classes  of 
animals.     All  the  alcoholic  dogs,  with  the  exception  of  the 
one  that  had  taken  the  smallest  amount,  had  the  distemper 
with  great  severity ;  all  the  normal  dogs  had  it  in  the  mildest 
possible  form. 

93.  Summary  of  Professor  Hodge's  conclusions.  —  Hence, 
we  may  conclude  from  these  experiments  that  alcohol,  when 
given  to  dogs,  even  in  moderation,  (1)  decreases  their  natural 
activity,    (2)  lessens  their   power   of   endurance   and  their 
ability  to  accomplish  things,  (3)  decreases  their  power  of 
resistance  to  disease,  and  (4)  increases  the  percentage  of 
deformity  and  of  death  among  their  offspring.     These  con- 
clusions have  a  most  important  bearing  on  the  general  sub- 
ject that  we  are  considering,  for  observations  show  that  sim- 


72  HUMAN  BIOLOGY 

ilar  effects  follow  even  the  moderate  use  of  liquor  by  human 
beings,  as  the  following  paragraphs  will  show. 

94.  Effect    of    the  moderate   use   of   alcohol    on   mental 
activity.  —  "  Few  causes  are  more  effective  in  leading  to  the 
abuse  of  alcohol  than  the  idea  that  when  one  finds  difficulty 
in  doing  a  thing  it  may  be  accomplished  more  easily  by  hav- 
ing recourse  to  beer,  or  wine,  or  whisky  for  their  '  stimulating ' 
effect.     In  general,  so  far  is  this  from  being  the  truth  that 
the  person  seeking  such  aid  is  really  using  a  hypnotic  and  a 
depressant.     Obviously  he  would  be  acting  more  wisely  to 
adopt  other  methods  of  accomplishing  his  end.     Nor  is  this 
conclusion   merely   theoretical.     Brain   workers   who   wish 
to  "  keep  a  clear  head  "  almost  universally  avoid  alcoholic 
drinks,  at  least  until  work  is  over.     And  even  among  those 
who  do  drink  it  is  customary  to  avoid  drinking  until  the 
day's  work  is  done."  l 

95.  Effect  of  a  moderate  use  of  alcohol  on  muscular  ac- 
tivity.—  That  the  general  effect  of  alcoholic  drinks  on  muscu- 
lar activity  is  a  depressant  rather  than  a  stimulant  was 
shown  by  experiments  on   English   soldiers   during  forced 
marches  in  Africa.     "  It  was  found  that  when  a  ration  of  rum 
was  served  out,  the  soldier  at  first  marched  more  briskly,  but 
after  about  three  miles  had  been  traversed  the  effect  of  it 
seemed  to  be  worn  off,  and  then  he  lagged  more  than  before. 
If  a  second  ration  were  given,  its  effect  was  less  marked,  and 
wore  off  sooner  than  that  of  the  first.     A  ration  of  beef  tea, 
however,  seemed  to  have  as  great  a  stimulating  effect  as 
one  of  rum,  and  not  to  be  followed  by  any  secondary  depres- 
sion." —  T.  LAUDER-BRUNTON. 

96.  Effect  of  a  moderate  use  of  alcohol  on  manual  dexter- 
ity. —  A  German  scientist  determined  the  effect  of  alcohol 

1  Hough  and  Sedgwick,  "The  Human  Mechanism." 


STIMULANTS  AND  NARCOTICS  73 

on  four  typesetters  in  the  following  way.  "  Four  days  were 
used  for  the  tests,  the  first  and  third  of  which  were  '  normal ' 
days ;  the  second  and  fourth  were  '  alcohol  days.' .  On  the 
alcohol  days  each  man  received  about  seven  ounces  of  a 
Greek  wine  ...  a  quarter  of  an  hour  before  the  trials 
took  place."  On  the  "  alcohol  days  "  it  was  found  that  the 
amount  of  type  set  was  on  the  average  15  per  cent  less  than 
that  set  on  the  "  normal  days." 

97.  Moderate  use  of   alcohol   in  relation   to   disease.  — 
"  A  much  larger  number  of  the  victims  of  alcoholic  intemper- 
ance die  of  some  infectious  disease  than  of  the  special  alco- 
holic infections.     Attention  has  been  repeatedly  called  in 
this  article  to  the  lowering  of  the  resistance  of  alcoholic 
patients  to  many  infectious  diseases.  .  .  .     This  lowered  re- 
sistance is  manifested  both  by  increased  liability  to  contract 
the  disease  and  by  the  greater   severity  of  the  disease."  — 
DR.  WELCH,  in  "  Physiological  Aspects  of  the  Liquor  Problem." 
Physicians  also  recognize  that  those  who  use  alcohol  are  more 
susceptible  to  pneumonia,  cholera,  and  other  diseases,  and 
that  the  percentage  of  recovery  of  such  patients  is  lower  than 
is  that  of  total  abstainers. 

98.  Total  abstinence  and  life  insurance.1  —  "  It  is  now 
becoming  generally  recognized  that  the  alcohol  habit  is  one 
of  the  main  factors  in  determining  length  of  life.     No  life 
office  will  knowingly  accept  the  proposal  of  any  one  known 
as  a  hard  drinker.     Evidence  of  a  very  striking  kind  is  rapidly 
accumulating,  which  shows  that  even  the  moderate  use  of 
alcohol  is  prejudicial  to  health  and  longevity.     In  England 
about  a  dozen  life  offices  recognize  this  fact  in  one  of  two 

1  These  quotations  were  furnished  the  authors  by  the  Equitable 
Life  Assurance  Society  of  the  United  States. 


74  HUMAN  BIOLOGY 

ways :  (1)  by  giving  a  reduction  of  premium  to  abstainers, 
or  (2)  by  awarding  them  a  larger  share  in  the  profits. 

"  Ten  years  ago  the  American  Temperance  Life  Insurance 
Association  was  formed  in  this  city  (N.  Y.),  and  accepts 
nothing  but  total  abstinence  risks.  It  has  had  pronounced 
success,  and  has  paid  something  like  $200,000  in  death 
claims.  President  Frank  Delano  states  that  the  results  of 
their  business  show  that  the  ratio  of  their  death  rate  to  that  of 
general  risks  is  about  26  per  cent  in  favor  of  the  total  abstainer." 
—  WILLIAM  E.  JOHNSON. 

99.  Business  arguments  for  total  abstinence.  —  The  value 
of  total   abstinence  as   a  business   asset  is  clearly  shown 
by  the  following  rules  of  railroads:     Rule  17,  New  York 
Central  &  Hudson  River  R.R. :  "  The  use  of  intoxicating 
drink  on  the  road  or  about  the  premises  of  the  corpora- 
tion is  strictly  forbidden.     No  one  will  be  employed,  or 
continued  in  employment,  who  is  known  to  be  in  the  habit 
of  drinking  intoxicating  liquor." 

Rule  H,  New  York,  New  Haven  &  Hartford  R.R. :  "  The 
use  of  intoxicants  by  employees  while  on  duty  is  prohibited. 
Their  habitual  use,  or  the  frequenting  of  places  where  they 
are  sold,  is  sufficient  cause  for  dismissal." 

General  Order  No.  12,  Delaware,  Lackawanna  &  Western 
R.R. :  "  The  use  of  intoxicants  while  on  or  off  duty,  or 
the  visiting  of  saloons  or  places  where  liquor  is  sold,  in- 
capacitates men  for  railroad  service,  and  is  absolutely  pro- 
hibited. Any  violation  of  this  rule  by  employees  in  engine, 
train,  yard,  or  station  service  will  be  sufficient  cause  for  dis- 
missal." 

100.  The  cost  of  intemperance.  —  The  following  figures, 
compiled  by  the  League  for  Social  Service  of  New  York  City 
from  the  United  States  Census,  present  some  very  striking 


STIMULANTS  AND  NARCOTICS  75 

facts  as  to  the  cost  to  our  country  of  the  abuse  of  alcohol. 
During  the  year  1880  (and  the  same  figures  would  doubtless 
hold  true  for  any  other  year),  it  was  found  that  three  fourths 
of  all  the  pauperism,  one  fourth  of  all  the  insanity,  and  three 
fourths  of  all  the  crime  in  the  United  States  were  directly 
caused  by  intoxicating  drinks.  Hence  if  the  use  of  intoxi- 
cating liquor  could  be  abolished,  the  heavy  expense  of  main- 
taining the  police  force,  the  criminal  courts,  insane  asylums, 
and  charity  organizations,  would  be  very  greatly  reduced. 

101.  Concluding  remarks  on   the   use   of   alcoholic  bev- 
erages. —  "  In  the  foregoing  pages  we  have  stated  the  sali- 
ent  facts   concerning   the   physiological   action   of  alcohol 
and  alcoholic  drinks.     It  only  remains  to  point  out  for  the 
student  the  obvious  conclusions  to  be  drawn  from  them  and 
from  the  long  and  on  the  whole  very  sad  experience  of  the 
race  with  alcoholic  drinks.     The  first  is  that,  except  in  sick- 
ness and  under  the  advice  of  a  physician,  alcoholic  drinks  are 
wholly  unnecessary,  and  much  more  likely  to  prove  harmful 
than  beneficial.     The  last  is  that  their  frequent,  and  especially 
their  constant,  use  is  attended  with  the  gravest  danger  to 
the  user,  no  matter  how  strong  or  self -controlled  he  may  be. 
.  .  .     The  only  absolutely  safe  attitude  toward  alcoholic 
drinks  is  that  of  total  abstinence  from  their  use  as  bever- 
ages." —  HOUGH  and  SEDGWICK,  "  The  Human  Mechanism." 

III.  TOBACCO 

102.  Effect   of  tobacco  on  growth.  —  In  discussing  the 
effects  of  tobacco,  it  is  important,  as  was  the  case  with  tea  and 
coffee,  to  distinguish  between  the  results  of  its  use  by  the 
young  and  by  adults.     Just  because  his  father  seems  to  be 
using  tobacco  without  harm  is  no  reason  why  a  boy  can  safely 
smoke.     We  have  already  called  attention  to  the  complex 


76  HUMAN  BIOLOGY 

composition  of  protoplasm.  During  the  whole  period  in 
which  the  body  is  attaining  its  growth  this  living  substance 
is  affected  far  more  appreciably  and  seriously  by  the  use 
of  stimulants  and  narcotics  than  is  the  case  later  in  life. 

Tobacco  is  a  narcotic  in  its  effects;  that  is,  it  tends  to 
decrease  activity  and  likewise  growth.  That  such  is  its 
effect  during  early  life  has  been  abundantly  proved  in 
many  ways.  But  perhaps  the  most  conclusive  facts  are 
those  presented  by  actual  measurements  made  in  college 
gymnasiums.  Dr.  Hitchcock,  of  Amherst  College,  who  has 
made  careful  measurements  of  college  students  for  a  good 
many  years,  finds  that  those  who  do  not  smoke  increase  in 
height  during  their  college  course  37  per  cent  more  than  those 
who  do  smoke,  and  in  chest  girth  this  difference  is  42  per  cent, 
or  nearly  one  half  as  much  again.  Dr.  Seaver  of  the  Yale 
Gymnasium  finds,  also,  that  in  height  and  lung  capacity 
smokers  are  considerably  inferior  to  those  who  do  not  use 
tobacco. 

103.  Effect  of  tobacco  on  mental  development.  —  Dr. 
George  L.  Meylan,  Director  of  the  gymnasium  of  Columbia 
University,  made  a  careful  comparison  during  two  years  of 
the  relative  physical  measurements,  rate  of  growth,  and 
scholarship  of  115  college  men  who  smoked  and  108  men 
in  the  same  class  who  were  non-smokers.1  He  found 
(1)  that  the  smokers  were  on  the  average  eight  months 
older,  which  means  that  they  had  entered  college  this  much 
later;  and  (2)  that  "  the  scholarship  standing  of  smokers 
was  distinctly  lower  than  that  of  the  non-smokers,"  showing 
"  that  the  use  of  tobacco  by  college  students  is  closely  asso- 
ciated with  idleness,  lack  of  ambition,  lack  of  application, 
and  low  scholarship." 

1  Popular  Science  Monthly,  August,  1910. 


STIMULANTS  AND  NARCOTICS  77 

"  Whatever  difference  of  opinion  there  may  be  regarding 
the  effect  of  tobacco  on  adults  —  and  much  difference  of 
opinion  exists  —  there  is  almost  complete  agreement  among 
those  best  qualified  to  know  that  the  use  of  tobacco  is  in  a 
high  degree  harmful  to  children  and  youths.  Physicians, 
teachers,  and  others  who  have  much  to  do  with  boys  very 
generally  remark  that  those  who  begin  to  smoke  at  an  early 
age  very  seldom  amount  to  much." 

Dr.  Andrew  D.  White,  for  twenty  years  President  of 
Cornell  University,  out  of  his  wide  experience  in  education, 
sums  up  the  matter  as  follows :  "  I  never  knew  a  student 
to  smoke  cigarettes  who  did  not  disappoint  expectations, 
or  to  use  a  vernacular  expression,  '  kinder  peter  out/  I  con- 
sider a  student  in  college  who  smokes  as  actually  handicap- 
ping himself  for  his  whole  future  career.  I  am  not  fanatical  in 
regard  to  smoking.  It  seems  to  me  possible  that  men  who 
have  attained  their  growth  and  are  in  full  health  and  strength 
may  not  be  injured  by  moderate  smoking  at  times.  I  will 
confess  to  you  that  at  one  period  of  my  life  I  was  a  smoker 
myself,  though  in  a  very  moderate  degree.  And  should  you 
feel  a  strong  desire  to  smoke,  thinking  it  may  rest  you  and 
change  happily  at  times  the  current  of  your  thought,  I  may 
perhaps  commend  to  you  my  own  example ;  for  I  began  my 
smoking  at  the  age  of  forty-five  and  ended  it  ten  years  ago 
at  the  age  of  seventy." 

104.  Tobacco  and  athletics.  —  One  of  the  rules  rigidly 
enforced  in  athletic  contests  is  that  all  candidates  must 
abstain  from  the  use  of  tobacco  while  in  training.  The 
reason  for  this  insistence  is  the  fact  that  tobacco  seriously 
interferes  with  the  action  of  the  lungs  and  heart ;  therefore, 
those  who  smoke  are  found  to  be  easily  "winded"  in  the 
games. 


78  HUMAN  BIOLOGY 

An  investigation l  has  been  recently  carried  on  among  the 
football  squads  of  fourteen  of  the  American  colleges  and  uni- 
versities to  determine  the  relative  success  of  the  smokers  and 
non-smokers  who  tried  for  positions  on  the  varsity  teams. 

"  Six  institutions  furnished  data  relating  to  the  '  try  outs.' 
A  total  of  210  men  contested  for  positions  on  the  first  teams  ; 
of  this  number  93  were  smokers,  and  117  were  non-smokers. 
Of  those  who  were  successful,  31  (i.e.  33  %)  were  smokers,  and 
77  (i.e.  65%)  were  non-smokers.  It  will  be  observed  that 
only  half  as  many  smokers  were  successful  as  non-smokers. ..." 

Hence,  the  ambitious  boy,  who  has  any  regard  for  develop- 
ing a  vigorous  body  fitted  for  athletic  success,  for  training 
a  mind  capable  of  clear  thinking,  and  for  preparing  himself 
for  a  successful  life  work,  will  resist  all  temptations  to  smoke, 
at  least  until  he  has  attained  his  full  growth. 

IV.  DRUGS  AND  PATENT  MEDICINES 

105.  Headache     powders.  —  Drugs     are    chemical    sub- 
stances used  in  the  preparation  of  medicines.     They  should 
never  be  taken  except  under  the  direction  of  a  competent 
physician.     Headache  medicines  usually  contain  some  chemi- 
cal (e.g.  acetanilid)  which  reduces  the  heart  action  and  so 
relieves  the  pain  by  diminishing  the  blood  pressure  without 
removing  the  cause  of  the  pain;  for  the  real  cause  may  be 
disordered   digestion   or   eye   strain.     Cases   of   permanent 
injury  and  even  of  death  have  resulted  from  taking  these 
headache  compounds  (Fig.  24). 

106.  Soothing  sirups   and   cough   medicines.  —  In   most 
soothing  sirups  and  cough  medicines  are  found   substances 
derived  from  opium,  which  is  a  powerful  narcotic.     Hence, 

1 "  Smoking  and  Football  Men."  —  Popular  Science  Monthly, 
October,  1912. 


STIMULANTS  AND  NARCOTICS  79 

children  who  are  given  soothing  sirups  often  become  stupefied. 
If  these  compounds  are  given  frequently,  they  injure  the 
child  permanently,  and  in  larger  doses  have  caused  death.  If 
cough  sirups  and  like  compounds  are  taken  often,  an  opium 


BEWARE   OF  ACETANILID 

A  large  proportion  of  the  most  common  head- 
ache medicines  sold  at  drug  stores  depend  for 
their  effectiveness  on  the  heart-depressing  ac- 
tion of  acetanilid.  In  some  cases  three  or  more 
grains  of  this  drug  are  present  in  each  dose. 

The  Pure  Food  and  Drug  Law  requires  all 
makers  of  patent  medicines  to  indicate  clearly 
on  the  labels  of  such  preparations  the  presence 
of  acetanilid  and  other  dangerous  compounds. 
Hence  one  has  but  to  read  the  labels  and  avoid 
these  nostrums  in  order  to  protect  himself. 

Take  no  headache  remedy  without  consulting  a 
doctor,  unless  you  are  sure  it  contains  no  acetanilid. 
Make  the  druggist  tell  you.  He  is  responsible.  A  suit 
for  damages  has  recently  been  won  against  a  New  York 
drug  store  for  illness  consequent  upon  the  sale  of  a 
"  guaranteed  harmless"  headache  tablet  containing  three 
grains  of  acetanilid. 


FIG.  24.  — Acetanilid  and  other  drugs  in  patent  medicines. 

habit  may  be  developed,  which  is  even  more  difficult  to  over- 
come than  is  the  alcohol  habit. 

107.  Patent  medicines  as  "bracers."  — Figure  25  repre- 
sents the  percentage  of  alcohol  contained  in  three  "  patent 
medicines"  as  given  by  the  Massachusetts  State  Board  of 


80 


HUMAN    BIOLOGY 


or 


o 


cc 


or 


V 


STIMULANTS  AND  NARCOTICS  81 

Health  in  published  document  No.  34,  as  compared  with  the 
percentages  of  alcohol  found  in  whisky,  champagne,  claret, 
and  beer.  The  stomach  bitters  (Fig.  25),  for  example,  con- 
tained over  eight  times  as  much  alcohol  as  that  found  in  beer. 
Hence,  the  average  drug  store  where  these  patent  medicines 
are  freely  sold  must  share  with  the  liquor  saloon  the  heavy 
responsibility  for  the  prevalence  of  the  drink  habit. 

108.  Pure  food  and  drug  law.  —  One  of  the  most  impor- 
tant laws  passed  by  the  59th  Congress  of  the  United  States 
was  that  which  compels  every  manufacturer  of  foods  or 
medicines  to  state  on  the  label  the  composition  of  each. 
Analyses  of  foods  and  drugs  have  proved  that  hitherto  many 
of  them  were  largely  adulterated  by  cheap  and  often  injurious 
compounds,  put  in  to  increase  the  manufacturers'  profits. 
Then,  too,  as  already  stated,  many  patent  medicines  contain 
high   percentages   of   alcohol   and   other   dangerous   drugs. 
Under  the  new  law, the  purchaser,  if  he  takes  the  trouble 
to  read  the  printed  label,  should  be  able  to  determine  exactly 
what  he  is  paying  for  and  putting  into  his  body. 

109.  Optional  home  work.  —  Examine  the  labels  on  any  patent 
medicine  bottles  or  boxes  you  can  find.    Make  a  list  of  such  com- 
pounds as  contain    alcohol,  opium,  morphine,  chloral,  acetanilid, 
or  phenacetin,  and  state  after  each  compound  the  percentage  of 
each  of  the  drugs  named. 


CHAPTER  V 

DIGESTION  AND  ABSORPTION  OF  THE  NUTRIENTS 
I.   GENERAL  SURVEY  OF  THE  DIGESTIVE  SYSTEM 


Necessity  of  digestion.  —  In  Chapter  III  we  dis- 
cussed the  composition,  uses,  and  the  preparation  of  foods. 
We  learned  in  our  study  of  plant  biology  (P.  B.,  Ch.  IV) 
that  certain  of  the  food  substances  will  readily  pass  through 
the  walls  of  plant  cells,  while  others  will  not.  Hence,  the 
latter,  to  become  available  for  use  in  other  cells,  must  be 
changed  to  soluble  form,  and  this  change  we  called  digestion. 
We  shall  now  discuss  similar  changes  that  take  place  in 
foods  within  our  bodies;  for  before  the  different  food  sub- 
stances can  reach  the  cells  of  the  brain>  the  muscles,  or  the 
bones  where  they  are  needed,  they  must  be  changed  from 
a  solid  or  semifluid  condition  into  liquids  that  can  pass 
through  the  walls  of  the  cells  that  lie  between  the  interior 
of  the  food  canal  and  the  blood.  These  necessary  changes 
-are  accomplished  within  our  bodies  in  the  alimentary  canal, 
a  complicated  tube  nearly  thirty  feet  in  length. 

111.  Parts  of  the  alimentary  canal.  —  The  alimentary 
canal  (Fig.  26),  as  in  the  other  vertebrates  studied,  begins 
with  the  mouth  opening  ;  it  enlarges  to  form  the  mouth  cavity, 
and  this  in  turn  communicates  behind  with  a  somewhat 
smaller  throat  cavity.  Below  the  throat  is  the  gullet,  which 
conducts  the  food  into  an  enlarged  pouch,  the  stomach.  Most 
of  the  lower  half  of  the  trunk  is  filled  with  the  much  coiled 

82 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       83 


intestines  which  begin  at  the  stomach  and  open  to  the  out- 
side of  the  body  at  the  lower  part  of  the  trunk. 


pylorus 


bile  duct 

transverse  colon  (cut) 
live: — 


common  orifice  of  bile 

and  pancreatic  ducts 

beginning  of  small 

intestine 


passage  from  nose  to  throat 

cavity  of  mouth 
throat  cavity 
opening  of  windpipe 


pancreatic  duct 


appendix 


FIG.  26.  —  Parts  of  the  alimentary  canal.  (The  liver  has  been  tilted  upward 
to  show  the  gall  bladder  on  its  lower  surface ;  a  piece  of  the  large  intes- 
tine has  been  removed  to  show  the  pancreas  behind  it.)  Compare  this 
figure  with  Fig.  2  which  shows  all  the  organs  in  position. 

112.    Digestive  glands.  —  Several  organs  that   are  neces- 
sary in  the  process  of  digestion,  as  already  discussed  in  the 


84  HUMAN  BIOLOGY 

fish  and  frog,  lie  outside  the  alimentary  canal  itself,  but  are 
connected  with  ito  These  are  the  digestive  glands.  They 
produce  digestive  ferments  (P.  B.,  53),  which  after  being 
dissolved  in  water  are  carried  into  the  food  canal  through 
small  pipes  or  ducts.  Thus  the  salivary  glands  pour  their 
secretions  into  the  mouth  cavity,  and  the  liver  and  pancreas, 
situated  near  the  stomach,  empty  their  juices  into  the  in- 
testine (Fig.  26). 

II.  THE  MOUTH  CAVITY  AND  ITS  FUNCTIONS 

113.    Study  of  the  mouth  cavity.  —  (Home  work.) 

Take  a  position  with  your  back  toward  a  window  or  some 
bright  light,  and  study  your  mouth  cavity  by  means  of  a  hand 
mirror. 

A.  Walls  of  the  mouth  cavity.  —  The  walls   that   are  rigid 

are  composed  largely  of  bone;  those  that  are 
yielding  are  largely  made  of  muscle. 

1.  Press  your  forefinger  against  the  roof,  the  side  walls, 

and  the  floor  of  the  mouth  cavity  beneath  the 
tongue  Which  walls  are  composed  of  bone? 
which  of  muscle  ? 

2.  What  is  the  color  of  the  inner  walls  of  the  mouth 

cavity?  This  color  is  due  to  the  blood  vessels 
that  lie  close  to  the  surface. 

3.  Rub  your  finger  over  the  mucous  membrane  which 

covers  these  walls.  The  substance  on  your  finger 
is  largely  mucus.  Describe  the  mucus  and  tell 
where  it  is  found. 

B.  Tongue. 

1.  To  what  part  of  the  mouth  cavity  is  the  tongue 

attached  ? 

2.  Chew  a  piece  of  apple  or  other  solid  food ;  note  and 

describe  the  action  of  the  tongue  during  the  process 
of  chewing  food. 

3.  Swallow  some  solid  food,  and  describe  the  action  of 

the  tongue  in  the  process  of  swallowing. 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       85 

114.  Structure  and  functions  of  the  tongue.  —  The  tongue 
is  an  elongated  mass  of  muscle  tissue  (Fig.  27).     The  muscle 
fibers   run   through    it   in  three    directions,   and   by   their 
separate  or  combined  action  the  free  end  of  this  organ  may 
be  moved  about  at 

will.  When  one  ex- 
amines the  mucous 
membrane  on  the 

upper  surface  of  the  jnl^-===^^ 

tongue,  it  is  possible 
to  see  elevations  of 
different  sizes,  called 
papilla.  Nerve  fi- 
bers carry  messages 
from  these  papillae 
to  the  brain,  and 
thus  we  become 
conscious  of  sen- 
sations of  taste. 
Among  the  carniv- 
ora  or  flesh-eating 
animals  the  papillae 
on  the  tongue  are 

especially  rigid.  This  enables  the  dog,  cat,  lion,  or  tiger  to 
scrape  the  meat  from  the  bones  and  to  extract  the  marrow 
after  the  bones  are  broken  open. 

115.  Study  of  the  teeth.  —  (Home  work.) 

1.   Bite  off  a  piece  of  apple  or  bread. 

a.   Describe  the  motion  of  the  jaws  in  biting  off  a  piece  of 

food. 
6.   In  what  part  of  each  jaw  are  found  the  teeth  that  are 

used  in  biting  food? 
c.    Describe  the  shape  and  cutting  surface  of  these  teeth. 


86 


HUMAN  BIOLOGY 


,  canine 


molars 


Chew  or  grind  a  piece  of  apple  or  bread. 

a.   Describe  the  motion  of  the  jaws  in  grinding  food. 

6.   In  what  part  of  each  jaw  are  found  the  teeth  that  are 

used  in  grinding  or  chewing  food  (Fig.  28)  ? 
c.   Describe   the  shape   and   grinding    surface    of    these 

teeth.  incLsora 

There  are  two  kinds  of 

cutting  or  biting 

teeth  (Fig.  28),  the 

incisors  (Latin,  in- 

cisum,  from  inddere       /^Hf^feS't^l^  ~~~~  bicuspids 

=  to  cut  into),  and 

the  canines  (Latin, 

canis  =  dog,    so- 
called  because  they 

often  resemble  the 

pointed  teeth  of  a 

dog). 
There  are  also  two  kinds  of  grinding  teeth,  the  bicuspids 

(Latin,  bi  =  two  -\-cuspis  =  point),  and  the  molars 

(Latin,  molaris  =  a  millstone). 

a.  (Optional.)  Human  teeth  may  be  obtained  from  a  dentist. 
They  should  be  cleaned  by  boiling  them  in  strong  caustic 
soda  solution,  then  in  water.  If  possible,  each  student 
'should  examine  and  draw  one  of  each  of  the  kinds  of 
teeth  named  above. 

6.  Determine  by  the  use  of  a  mirror  the  number  of  teeth 
of  each  kind  that  you  have  and  record  the  numbers 
in  a  table  in  your  notebook  as  follows  :  — 


FIG.  28.  — Teeth  in  upper  jaw. 


RIGHT  HALF  OF 
UPPER  JAW 

LEFT  HALF  OF 
UPPER  JAW 

RIGHT  HALF  OF 
LOWER  JAW 

LEFT  HALF  OF 
LOWER  JAW 

Incisors.     .     . 

Canines     .     . 

Bicuspids  .     . 
Molars  .     .     . 

• 

DIGESTION  AND  ABSORPTION   OF  NUTEIENTS       87 

4.  Examine  carefully  each  of  the  teeth  in  your  mouth  and 
indicate  ir^  a  table  like  the  following  the  number  of 
cavities  (unfilled)  and  the  number  of  fillings  that 
you  find. 


RIGHT  HALF  OF 
UPPER  JAW 

LEFT  HALF  OF 
UPPER  JAW 

RIGHT  HALF  OF 
LOWER  JAW 

LEFT  HALF  OF 
LOWER  JAW 

Cavity 

Filling 

Cavity 

Filling 

Cavity 

Filling 

Cavity 

Filling 

Incisors    .     . 

Canines   . 

Bicuspids 
Molars     .     . 

116.  Arrangement  of  the  teeth.  —  Within  the  mouth 
cavity  the  solid  food  is  cut  into  small  pieces,  mixed  with 
the  juices  of  the  mouth,  and  then 
ground  into  a  pulpy  mass.  A 
large  part  of  this  work  is  done 
by  the  teeth,  which  are  arranged 
in  two  semicircular  arches  (Fig. 
29).  In  a  normal  set  of  teeth 
each  tooth  in  the  lower  jaw  works 
against  a  corresponding  tooth  in 
the  upper  jaw,  and  this  is  very 
necessary  in  order  to  chew  the  food  properly  and  to  keep  teeth 
and  gums  in  a  healthy  condition.  If,  however,  the  teeth  do 
not  develop  as  described  above,  a  competent  dentist  should 
be  employed  to  correct  the  irregularities. 


FIG.  29. — Arrangement  of  the 
teeth. 


117.   Milk   teeth.  —  During   early   childhood    there   appears   a 
first  set  of  milk  teeth,  which  later  are  gradually  loosened  and  dis- 


88 


HUMAN  BIOLOGY 


placed  by  the  growth  of  the  permanent  set.     There  are  but  twenty 
teeth  in  the  milk  set  and  their  arrangement  if1,  as  follows  :  — 


RIGHT  HALF  OF 

LEFT  HALF  OF 

RIGHT  HALF  OF 

LEFT  HALF  OF 

UPPER  JAW 

UPPER  JAW 

LOWER  JAW 

LOWER  JAW 

Incisors     .     .     . 

2 

2 

2 

2 

Canines    .     .    . 

1 

1 

1 

1 

Molars      .     .     . 

2 

2 

2 

2 

namel 


entine 


Bicuspids  are,  therefore,  wanting,  and  the  milk  molars  occupy  the 
position  in  each  half  jaw  that  later  is  rilled  by  the  two  bicuspids 

of  the  permanent  set.     The  teeth 
appear  gradually,   the  lower  inci- 
sors usually  being  the  first  to  push 
through  the  gums  at  about  the  sixth 
month.     The  third  permanent  mo- 
pulp    lars  of  each  half  jaw  often  appear 
cavity  as  jate  as  the  twentieth  year ;  they 
are  called  the  wisdom  teeth. 

118.   Structure  of  teeth. — The 

exposed  portion  of  a  tooth  is 
called  the  crown  (Fig.  30).  It  is 
covered  with  a  layer  of  enamel, 
which  is  the  hardest  tissue  in  the 
body.  The  root  of  the  tooth  is 
imbedded  in  a  socket  in  the  bone 
of  the  jaw.  It  has  no  enamel, 

but,  instead,  its  outer  layer  is  a 

modified  bone  tissue   called  ce- 

FIG.  30.  —  Longitudinal  section  of  .       mr      •  i 

a  canine  tooth.  ment.     The  incisors  and  canines 

usually  have  but  a  single  root, 

the  bicuspids  may  have  two,  and  the  molars  are  often  held  in 
the  jawbone  by  three,  four,  or  five  roots.     In  the  region  be- 


neck 


root 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       89 

tween  the  crown  and  the  root  is  the  neck  of  the  tooth,  which 
is  surrounded  by  the  gums. 

The  internal  structure  of  the  tooth  is  well  shown  in  a  verti- 
cal section  (Fig.  30).  The  covering  of  enamel  is  thickest 
over  the  top  of  the  crown;  it  becomes  thinner  down  the 
exposed  sides,  and  disappears  in  the  neck  region.  The  largest 
part  of  the  tooth  is  composed  of  bony  dentine.  In  the  central 
part  is  the  pulp  cavity.  This  region  is  well  supplied  with 
nerves  and  blood  vessels,  which  enter  through  a  small  open- 
ing at  the  end  of  each  root.  The  blood  furnishes  the  teeth 
with  new  building  material. 

119.  Care  of  the  teeth.  —  Too  much  stress  cannot  be 
laid  on  the  importance  of  caring  for  the  teeth,  since  decay- 
ing teeth  are  frequently  painful,  are  always  unsightly,  are 
usually  the  cause  of  an  ill-smelling  breath,  and  often  lead  to 
indigestion.  Immediately  after  eating,  one  should  remove 
any  bits  of  food  from  between  the  teeth  by  using  a  wooden 
toothpick,  dental  floss,  or  thread.  Pins,  knife-blades,  or 
other  metallic  implements  should  never  be  used  for  this 
purpose.  The  teeth  should  then  be  brushed  thoroughly 
on  all  sides,  and  warm  .water  and  a  little  castile  soap  or 
reliable  tooth  powder  should  be  used.  The  sides  of  the  teeth 
should  be  brushed  from  the  gums  toward  the  crown  in  order 
to  avoid  pushing  the  gums  away  from  the  neck  of  the  tooth. 

Since  the  enamel  that  covers  the  crown  of  tire  tooth  is 
composed  entirely  of  mineral  matter,  it  cannot,  of  course, 
decay.  If,  however,  food  is  allowed  to  decompose  on  or 
between  the  teeth,  the  acids  formed  by  the  action  of  the 
bacteria  gradually  dissolve  the  enamel  until  a  cavity  is 
formed.  When  the  dentine  is  reached,  the  bacteria  directly 
cause  this- part  of  the  tooth  to  decay,  since  it  contains  living 
matter. 


90  HUMAN  BIOLOGY 

The  teeth  ought  never  to  be  used  to  crack  nuts  or  to  bite 
hard  substances,  for  while  the  enamel  is  a  very  hard  sub- 
stance, it  is  also  brittle  and  may  be  cracked  or  broken  off 
by  such  treatment.  If  once  lost,  it  will  not  grow  again. 
It  is  evident,  therefore,  that  it  is  very  essential  to  protect 
this  outer  layer,  both  from  the  action  of  acids,  and  from 
mechanical  injuries. 

Some  people  seem  to  think  that  the  loss  of  natural  teeth 
is  not  a  very  serious  matter,  and  that  false  teeth  are  just 
as  effective  as  those  teeth  provided  by  nature.  Experi- 
ments have  shown,  however,  that  the  power  to  crush  food  with 
false  teeth  is  only  about  one  fifth  that  of  the  power  exerted 
by  a  normal  set  of  teeth.  Hence,  loss  of  teeth  is  very  likely 
to  result  in  imperfect  mastication  of  food,  with  consequent 
ill-health  resulting  from  indigestion.  If,  however,  one  has 
been  unfortunate  enough  to  have  lost  one  or  more  teeth, 
the  gaps  should  be  promptly  filled  by  bridge  work.  The 
teeth  should  be  examined  by  a  dentist  at  least  twice  a  year 
so  that  any  cavities  found  may  be  promptly  filled.  In  short, 
everything  possible  should  be  done  to  secure  and  preserve  a 
beautiful  and  effective  set  of  teeth. 

120.  Importance  of   the    digestion  of    starch.  —  In   47  of 

"  Plant  Biology  "  we  proved  that  starch  can  not  pass  through 
the  walls  of  cells,  and  we  likewise  showed  in  49  how  this 
food  substance  is  made  ready  by  the  process  of  digestion 
to  pass  through  membranes.  Many  of  the  foods  we  eat 
contain  large  percentages  of  starch.  We  are  now  to  show 
experimentally  how  starch  is  digested  in  the  human  body. 

121.  Does  saliva  digest  starch?  —  Laboratory  demonstra- 
tion, t 

Prepare  some  starch  paste  by  boiling  in  a  test  tube  of 
water  an  amount  of  arrowroot  starch  (or  corn  starch,  if 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       91 

the  arrowroot  cannot  be  obtained)  equal  to  half   the   size 
of  a  pea. 

1.  Pour  a  small  amount  of  the  starch  paste  into  a  test  tube, 

add  some  Fehling's  solution,  and  boil.  Is  grape 
sugar  present ?  How  do  you  know? 

2.  Put  some  saliva  into  a  clean  test  tube.     Test  it  with 

Fehling's  solution  as  you  did  the  starch.  Does  this 
saliva  contain  grape  sugar  ?  How  do  you  know  ? 

3.  In  another  clean  test  tube  pour  some  saliva  into  some  of 

the  starch  paste,  shake  the  mixture,  and  warm  it 
gently  for  a  few  moments  to  the  same  temperature 
as  that  of  the  mouth.  Now  test  with  Fehling's 
solution,  as  in  1  above. 

a.  State  what  was  done,  the  result,  and  the  conclusion. 

b.  What,  therefore,  is  the  effect  of  saliva  on  boiled  starch  ? 

c.  Name  several  foods  already  studied  that  could  be 

partially  digested  by  saliva. 

4.  (Optional  home  work.)     Take  some  popped  corn  or  shredded 

wheat  into  the  mouth  and  chew  it  thoroughly.  Can  you 
detect  any  sweet  taste  at  first?  Can  you  after  chewing 
for  a  time  ?  What  does  this  experiment  teach  you  as  to 
one  advantage  of  thoroughly  chewing  the  food  ? 

122.  Position  and  action  of  the  salivary  glands.  —  In  addition  to 
the  mucus  given  out  by  the  mucous  membrane  (113)  the  mouth 
receives  another  secretion  called  saliva.  At  the  sight  or  smell  of 
tempting  food  "the  mouth  waters."  Saliva  is  secreted  by  the 
salivary  glands.  Two  of  these  glands  (the  parotids,  from  Greek, 
meaning  "beside  the  ear")  are  located  near  the  back  of  the  lower 
jawbone  just  beneath  and  in  front  of  the  ear.  Any  one  who  has 
had  the  mumps  can  readily  locate  these  organs,  for  mumps  is  a 
disease  in  which  these  glands  swell.  From  the  parotid  gland  of  each 
side  a  duct  conveys  saliva  along  through  the  walls  of  the  cheek. 
This  duct  opens  at  the  top  of  a  small  elevation,  which  may  be  felt 
with  the  tip  of  one's  tongue  opposite  the  upper  second  molar  teeth. 

Two  other  pairs  of  glands  (the  submaxillary,  Latin,  sub  =  be- 
neath +  maxilla  =  jawbone,  and  the  sublingual,  Latin,  sub  = 


92  HUMAN  BIOLOGY 

beneath  +  lingua  =  tongue)  lie  in  the  muscular  floor  of  the  mouth 
cavity,  and  the  ducts  from  these  glands  open  in  the  floor  of  the  mouth 

under  the  tongue. 

i 

123.  Uses  of    saliva.  —  (1)   The  saliva  aids  the  mucus 
in   keeping   the   mouth  moist,  and   thus    we    are    enabled 
to  talk  easily.     (2)    It  moistens  the  food  for  swallowing. 
The   importance  of  this  function  is  appreciated  when  one 
tries  to  hurry  in   swallowing   the    crumbs  of   dry  cracker. 
(3)  Saliva  helps  to  dissolve  sugar  and  salt,1  thus  enabling 
us  to  taste  them.     If  the  tongue  is  wiped  dry  and  a  piece  of 
sugar  is  placed  upon  it,  we  have  no  sensation  of  taste  until 
the  sugar  has  been  partially  dissolved  by  the  mixture   of 
saliva  and  mucus  that  is  poured  upon  it.     (4)  Besides  the 
three  mechanical  functions  of  saliva  that  we  have  just  enu- 
merated, this  secretion  digests  cooked  starch,  as  we  have 
already  shown.     This  digestive  action  is  due  to  a  ferment 
known  as  ptyalin  (pronounced   ty'alin)  which  acts  in  the 
same  manner  as  the  diastase  found  in  plants. 

III.   THE  THROAT  CAVITY  AND  GULLET  AND  THEIR 
FUNCTIONS 

124.  Structure  of  the  throat  and  gullet.  —  The  cavity  of  the 
throat  is  behind  the  mouth.     If  one  holds  a  mirror  in  front  of  the 
mouth  opening  and  presses  down  upon  the  tongue  with  a  spoon, 
one  sees  hanging  down  a  small,  fingerlike  extension  of  the  soft 
palate,  called  the  uvula.    When  food  is  swallowed,  this  little  tongue 
of  the  soft  palate  is  shoved  backward  into  a  horizontal  position, 
where  it  helps  to  separate  the  throat  cavity  from  the  -nose  cavity. 

The  lower  part  of  the  throat  narrows  into  the  gullet.  This  tube 
traverses  the  length  of  the  chest  cavity,  and  as  it  nears  the  stomach, 
it  passes  through  the  diaphragm.  Like  all  other  parts  of  the  ali- 
mentary canal  it  is  lined  with  mucous  membrane,  which  furnishes  a 

1  See  130,  A,  1. 


DIGESTION  AND  ABSORPTION   OF  NUTRIENTS       93 

soft,  moist  surface  for  the  passage  of  food.     Outside  the  mucous 
membrane  are  rings  of  circular  muscle  running  around  the  gullet. 

125.  Functions  of  the  throat  and  gullet.  —  The  food  is  quickly 
forced  out  of  the  throat  cavity  into  the  gullet,  and  is  pushed  slowly 
down  the  gullet  by  the  successive  contractions  of  the  rings  of  muscle 
just  described.  After  being  swallowed  from  the  throat,  the  food 
does  not  drop  into  the  stomach,  for  the  walls  of  the  gullet  are 
pressed  together  by  surrounding  organs,  except  when  this  tube  is 
opened  by  the  passing  food.  In  fact,  after  practice,  one  can  swallow 
when  standing  on  one's  head,  and  most  quadrupeds  (horse,  dog,  cow), 
when  feeding,  hold  the  head  below  the  level  of  the  stomach. 


IV.  THE  STOMACH  AND  ITS  FUNCTIONS 

126.  Position,   size,   shape.  —  The  stomach  is  a  curved 
muscular  pouch,  which  lies  about  midway  between  the  upper 
and  lower  ends  of  the  trunk,  with  its  larger  end  lying  toward 
the  left  side  of  the  body,  where  it  communicates  with  the 
gullet  (Fig.  26).     When  moderately  filled,  this  organ  holds 
3J  to  4  quarts.     The  small  intestine  is  con- 
tinuous with  the  right  end  of  the  stomach, 

the  communication  between  the  two  (known 
as  the  pylorus,  from  Greek,  meaning  gate- 
keeper) being  controlled  by  a  ring  of 
muscle. 

127.  The  lining  of  the  stomach  and  the 
gastric   glands.  —  If   one   examines   with   a 
lens  the  mucous  lining  of  the  stomach,  a 
countless    number    of    small    openings    are 
seen   which    look    like    pin   pricks.     These 
are  the   pores  through   which   a  digestive 

fluid  known  as  gastric  juice  is  discharged  from  the  gastric 
glands  (Fig.  31).     This  digestive  fluid  is  composed  of  water 


FIG.  31.  —  Three 
gastric  glands. 


94  HUMAN  BIOLOGY 

(over  99  per  cent),  free  hydrochloric  acid  and  a  digestive  fer- 
ment called  pepsin. 

128.  Muscles  of  the  stomach.  —  The  chief  function  of  the 
human  stomach  is  to  secrete  the  gastric  juice  and  to  mix  this 
juice  thoroughly  with  the  food.     The  muscular  walls  are 
well  adapted  for  this  purpose.     When  the  food  reaches  the 
stomach,  the  gastric  juice  oozes  out  upon  it,  and  the  mixture 
is  pushed  back  and  forth  and  up  and  down  by  the  successive 
action  of  the  different  layers  of  muscles.     The  return  of  the 
food  to  the  mouth  cavity  is  prevented  by  the  contraction  of 
the  circular  muscles  at  the  lower  end  of  the  gullet,  except 
in  the  case  of  nausea,  when  they  relax  and  allow  the  stomach 
to  rid  itself  of  its  contents.    The  circular  muscle  at  the  pyloric 
end  of  the  stomach  (Fig.  26)  relaxes  from  time  to  time,  and 
the  partially  digested  food  is  pushed  on  into  the  intestine. 

Fortunately  for  the  well-being  of  the  body,  all  these  pro- 
cesses are  entirely  automatic;  that  is,  they  are  carried  on 
-without  our  conscious  direction.     The  muscles  of  the  ali- 
mentary canal  for  this  reason  are  called  involuntary  (Latin, 
in  =  without  +  voluntas  =  will) . 

129.  Digestion  in  the  stomach.  —  The  gastric  juice   has 
practically  no  effect  on  the  nutrients  starch  and  fat.     The 
saliva,  however,  that  is  mixed  with  the  food  and  swallowed 
with  it  continues  to  act  upon  the  starch  for  a  time,  particu- 
larly in  the  upper  part  of  the  stomach.     Sugars  and  soluble 
salts  (that  is,  salts  that  dissolve  in  water) ,  if  not  dissolved  in 
the  mouth,  are  readily  liquefied  by  the  water  of  the  gastric 
juice.     Certain  mineral  food  substances,  however,  like  phos- 
phate of  lime  found  in  milk,  are  not  soluble  in  water,  and  these 
insoluble  salts  reach  the  stomach  unchanged.     The  following 
experiment  illustrates  the  way  in  which  mineral  matters 
are  made  liquid  by  the  hydrochloric  acid  in  the  gastric  juice. 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       95 

130.  Digestion   of  mineral  matters.  —  (Optional.)      Laboratory 
demonstration. 

Note  to  Teacher:  Part  A  should  be  demonstrated  in  connection 
with  the  study  of  saliva ;  Part  B;  in  connection  with  gastric  diges- 
tion. 

Materials:  Table  salt,  phosphate  of  lime,  diluted  hydrochloric 
acid  (one  part  acid  to  six  parts  water). 

A.  Soluble  mineral  matters. 

1.  Put  some  table  salt  into  a  test  tube,  add  water,  and  shake 

well.     Does  the  salt  dissolve  ?    How  do  you  know  ? 

2.  Saliva  is  largely  (over  99  per  cent)  composed  of  water. 

How,  then,  are  soluble  mineral  matters  made  liquid  in 
the  mouth  ? 

B.  Insoluble  mineral  matters. 

1.  Put  some  insoluble  mineral  matter  like  phosphate  of  lime 

(which  is  one  of  the  constituents  of  milk)  into  a  test 
tube,  add  water,  and  shake  well,  then  allow  the  tube 
to  stand  for  a  tune  before  answering  the  following 
questions. 

a.  Does  phosphate  of  lime  dissolve  in  water  ?  How  do  you 
know  ?  Why  is  phosphate  of  lime  called  an  insoluble 
mineral  matter  ? 

6.  Shake  the  mixture  again  and  add  some  diluted  hydro- 
chloric acid.  What  change  do  you  observe  ? 

2.  Hydrochloric  acid  is  one  of  the  ingredients  of  gastric  juice. 

How,  then,  are  insoluble  mineral  matters  like  phos- 
phate of  lime  digested  in  the  stomach  ? 

131.  Digestion  of  proteins.  —  One  of  the  most  important 
actions  which  takes  place  in  the  stomach  is  the  digestion  of 
proteins.     This  class  of  nutrients  is  not  readily  soluble  in 
water  and  so  cannot  pass  through  the  walls  of  cells  (P.  B.,  52). 
Hence,  before  proteins  can  be  made  available  for  use  in  the 
body  they  must  be  changed  to  a  soluble  form  known  as 


96  HUMAN  BIOLOGY 

peptone  (P.  B.,  53).     This  chemical  change  is  brought  about 
in  our  bodies  to  some  extent  by  the  gastric  juice. 

132.  Digestion  of  proteins.  —  Optional  laboratory  demonstra- 
tion. 

Materials:  Boiled  egg,  powdered  pepsin  (which  should  be  ob- 
tained fresh  or  kept  in  a  tightly  stoppered  bottle),  hydrochloric 
acid,  water ;  test  tubes.  Each  of  the  following  experiments  should 
be  kept  throughout  the  whole  time  as  nearly  as  possible  at  the 
temperature  of  the  body  (98.6°  F.). 

A.  To  prove  that  protein  requires  digestion  after  it  is  swallowed. 

1.  .Shave  off  with  a  knife  and  cut  into  the  finest  pieces  possible  a 

part  of  the  white  of  a  boiled  egg  (or  better,  grate  the 
egg).  The  solid  constituents  of  egg  are  largely  pro- 
tein. Put  into  a  test  tube  a  small  amount  (about  twice 
the  size  of  a  pea)  of  this  minced  egg,  add  water,  and 
shake.  Label  the  test  tube  No.  1,  and  allow  the  mix- 
ture to  stand  for  a  day  or  two  as  nearly  as  possible  at 
a  temperature  of  98.6°  F.  (which  is  the  normal  tem- 
perature of  the  interior  of  our  bodies). 

a.  Has  all  the  egg  been  made  liquid  or  digested  by  the 

water  ?    How  do  you  know  ? 

b.  Pour  off  some  of  the  clear  liquid  into  a  test  tube,  and  add 

nitric  acid  and  boil.  Has  any  of  the  protein  been 
digested  ?  How  do  you  know  ? 

2.  Into  another  test  tube  put  the  same  amount  of  minced  egg, 

add  a  spoonful  or  more  of  saliva.  Label  it  test  tube 
No.  2.  Shake  and  allow  it  to  stand  for  a  day  or  two 
beside  test  tube  No.  1. 

a.  Is  protein  digested  by  saliva  ?    How  do  you  know  ? 

b.  What  do  you  therefore  conclude  in  regard  to  the  possibility 

of  protein-digestion  by  the  saliva  ? 

B.  To  prove  that  gastric  juice  digests  protein. 

1.   Into  a  third  test  tube  put  a  small  amount  of  the  minced  egg. 
Half  fill  the  tube  with  water,  add  powdered  pepsin  to 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       97 

the  amount  equal  to  about  the  size  of  a  pea,  and  also 
add  five  to  ten  drops  of  diluted  hydrochloric  acid. 
(Water,  pepsin,  and  hydrochloric  acid  are  the  three 
principal  ingredients  of  gastric  juice.)  Label  the  test 
tube  No.  3,  shake  the  mixture,  and  put  it  in  a  warm 
place  beside  test  tubes  1  and  2.  (Since  it  is  difficult 
to  get  the  exact  proportion  of  the  three  ingredients  of 
gastric  juice,  it  is  well  to  prepare  several  tubes  as  de- 
scribed above,  labelling  each  test  tube  No.  3.)  At  the 
end  of  a  few  hours  or  a  day  examine  the  test  tubes  con- 
taining the  minced  egg  and  the  artificial  gastric  juice, 
comparing  them  with  test  tubes  1  and  2.  Has  the  egg 
been  digested  ?  How  do  you  know  ? 

V.  THE  SMALL  INTESTINE  AND  ITS  FUNCTIONS 

133.  Position,  form,  and  size.  —  The  small  intestine  is  a 
much-coiled  tube,  filling  the  larger  portion  of  the  abdominal 
cavity  (Fig.  2).     It  is  usually  twenty  feet  or  more  in  length, 
and  therefore   constitutes  nearly  four  fifths  of  the  whole 
length  of  the  alimentary  canal.     Beginning  at  the  stomach, 
it  decreases  somewhat  in  size  until  it  opens  into  the  large 
intestine. 

134.  Peritoneum.  —  The  whole  abdominal  cavity  is   lined  with 
thin,  smooth  membrane  called  the  peritoneum.     Sheets  of  peritoneum 
likewise  inclose  the  various  organs  found  in  the  abdominal  cavity, 
and  help  to  connect  these  organs  to  the  walls  of  the  abdomen. 
Peritonitis  is  an  inflammation  of  any  portion  of  this  membrane. 

135.  Digestion  in  the  small  intestines.  —  In  the  intestines 
important  digestive  processes  are  carried  on  (1)  by  the  juices 
secreted  in  the  glands  found  in  the  inner  wall  of  the  intestine 
(intestinal  glands),  (2)  by  the  pancreatic  juice  secreted  by  the 
pancreas,  and  (3)  by  the  bile  secreted  by  the  liver.     All 
these  juices,  when  mixed  with   the  food   in  the  intestine, 


98  HUMAN  BIOLOGY 

bring  about  the  digestion  of  fats  and  complete  the  digestion 
of  starch  and  proteins. 

The  pancreas  (Fig.  26)  lies  just  below  the  stomach  and  extends 
from  the  region  of  the  pylorus  toward  the  left  side  of  the  body. 
Within  the  gland  is  secreted  the  pancreatic  juice,  which  is  poured  out 
through  a  duct  upon  the  food  just  after  it  enters  the  small  intestine. 
Pancreatic  juice  digests  three  of  the  nutrients;  namely,  starch,  pro- 
teins, and  fats.  Like  saliva,  pancreatic  juice  changes  starch  into 
sugar,  and  like  gastric  juice,  it  converts  proteins  into  peptones. 
The  heat  of  the  body  melts  much  of  the  fat  before  it  reaches  the  in- 
testine, but  this  liquid  cannot  be  absorbed  until  it  has  been  still 
further  acted  upon  chemically  by  the  pancreatic  juice  and  bile. 

VI.    THE  LARGE  INTESTINE  AND  ITS  FUNCTIONS 

136.  Position,  form,  and  size.  —  The  large  intestine  is  the  last 
portion  of  the  alimentary  canal.     It  is  a  tube  five  or  six  feet  long, 
with  a  gradually  decreasing  diameter.     Beginning  in  the  lower  right- 
hand  region  of  the  abdominal  cavity  as  a  sac-like  pouch  (Fig.  26), 
the  large  intestine  passes  upward  on  the  right  side  of  the  body  cavity 
to  the  lower  surface  of  the  stomach ;  it  then  crosses  the  abdominal 
cavity ;  a  third  portion  continues  downward  on  the  left  side.     The 
large  intestine  then  takes  an  S-shaped  course  and  passes  to  the  ex- 
terior of  the  body  by  a  short,  straight  tube. 

137.  Vermiform  appendix.  —  On  the  right  side  of  the  body,  and 
connected  with  the  beginning  of  the  large  intestine,  is  a  small,  tubular 
sac  about  the  size  of  a  lead  pencil,  and  usually  about  four  inches 
long  (Fig.  26).     From  its  more  or  less  twisted  shape  it  has  received 
the  name  vermiform  appendix  (Latin,  vermiform  =  worm-shaped). 
Appendicitis  is  a  diseased  condition  arising  from  inflammation  in  the 
tissues  of  the  appendix. 

VII.  ABSORPTION  FROM  THE  ALIMENTARY  CANAL 

138.  Necessity   for   the   absorption   of  food.  —  We  have 
now  learned  something  of  the  processes  of  digestion.     We 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS       99 

have  seen  that  the  foods  we  eat  are  ground  up  in  the  mouth 
cavity  by  the  teeth  and  thus  made  ready  for  the  action  of  the 
various  digestive  juices.  We  have  also  demonstrated  that 
sugars  and  soluble  salts  are  dissolved  in  the  mouth;  that 
insoluble  mineral  matters  are  made  soluble  in  the  stomach; 
that  starch  is  changed  to  sugar  by  the  saliva  and  pancreatic 
juice;  that  proteins  are  converted  into  peptones  by  the 
pancreatic  and  gastric  juices ;  and  that  fats  are  digested  in 
the  intestines  by  the  combined  action  of  bile  and  pancreatic 
juice.  Were  the  food  to  remain  within  the  alimentary 
canal,  however,  even  though  it  had  been  thoroughly  digested, 
it  would  still  be,  in  a  certain  sense,  outside  the  body,  since 
this  canal  is  a  continuous  tube  opening  to  the  exterior  at 
either  end.  In  order  to  furnish  material  for  building  and 
repairing  the  various  tissues,  the  liquid  nutrients  must  be 
distributed  to  the  tissues  wherever  needed.  This  is  accom- 
plished through  the  agency  of  the  blood  system.  We  have 
now  to  consider  the  process  of  absorption,  which  includes  the 
final  steps  whereby  foods  become  a  part  of  blood.  By  absorp- 
tion is  meant  the  passage  of  the  digested  food  through  the  lining 
of  the  alimentary  canal,  and  through  the  thin  walls  of  the  count- 
less blood  vessels  that  lie  close  at  hand. 

139.   Absorption  in  the   mouth,   throat,  gullet,  and   stomach.  — 

While  the  mouth,  throat,  and  gullet  all  have  a  moist  lining,  gener- 
ously supplied  with  thin-walled  blood  vessels,  relatively  little  ab- 
sorption takes  place  in  these  regions;  first,  because  only  a  small 
amount  of  the  food  has  been  digested,  and  secondly,  because  the  food 
does  not  remain  long  enough  in  these  organs  for  absorption  to  take 
place. 

The  food  usually  remains  in  the  stomach  for  several  hours,  and 
one  would  naturally  expect  that  a  good  deal  of  absorption  would 
take  place  during  this  time.  But  we  must  remember  that  the  con- 
traction of  the  stomach  muscles  keeps  the  food  in  constant  motion. 


100  HUMAN  BIOLOGY 

This  movement,  while  favorable  to  digestion,  diminishes  absorp- 
tion, because  the  liquefied  food  does  not  remain  long  enough  in  one 
place  to  be  absorbed  by  the  blood. 

140.  Absorption  in  the  small  intestine.  —  We,  therefore, 
find  that  most  of  our  food  passes  through  the  pylorus  before 
it  is  absorbed.  In  the  structure  of  the  small  intestine,  how- 
ever, we  seem  to  find  every  possible  provision  for  gathering 
up  the  nutrients.  In  the  first  place,  the  lining  of  this  tube  at 
intervals  is  elevated  to  form  ridges  that  run  two  thirds  of 
the  way  around  the  interior  wall,  and  some  of  them  project 
about  a  third  of  an  inch  into  the  cavity  of  the  intestines 
(Fig.  2).  Like  little  dams,  they  delay  the  onward  flow  of 
the  food,  and  they  also  increase  considerably  the  large  surface 
for  absorption. 

The  absorbing  surface  is  multiplied  still  further  by  the 
villi.  If  one  were  to  examine  with  a  hand  lens  the  mucous 
lining  of  the  small  intestine,  one  would 
see  that  the  ridges  and  the  depressions 
are  covered  with  tiny,  hairlike  pro- 
cesses that  give  a  velvety  appearance 
to  the  surface.  Each  of  these  minute 
elevations  is  called  a  villus  (Latin,  villus 
=  a  tuft  of  hair).  The  villi  are  ex- 
ceedingly numerous  in  the  small  intes- 
tine of  man,  the  total  number  being 
FIG.  32.— Two  vmi,  highly  estimated  at  four  millions.  The  ab- 

magmfied. 

sorbent  action  of  the  villi  may  be  com- 
pared with  the  absorption  that  takes  place  through  the 
walls  of  the  root  hairs  of  plants.  In  structure,  however, 
a  villus  is  much  more  complicated  than  is  a  root  hair. 

Each  villus  (Fig.  32)  when  highly  magnified,  is  found  to 
contain  a  network  of  minute  blood  vessels,  and  since  they  are 
covered  only  by  a  thin  layer  of  cells  on  the  outside  of  the 


DIGESTION  AND  ABSORPTION   OF  NUTRIENTS      101 

villus,  the  liquefied  food  is  readily  absorbed  by  the  blood 
current.  Within  the  villi,  too,  are  other  thin-walled  tubes, 
called  lacteals,  which  are  of  great  importance  in  the  absorption 
of  fats.  As  the  souplike  mass  of  food  is  pushed  slowly 
along  through  the  small  intestine,  it  becomes  less  and  less 
in  bulk,  and  more  and  more  solid,  owing  to  the  fact  that  the 
dissolved  salts,  sugars,  peptones,  and  fats  are  largely  taken  up 
by  the  blood  vessels  and  lacteals  within  the  villi. 

141.  Absorption  in  the  large  intestine.  —  The  amount  of  absorp- 
tion in  the  large  intestine  is  considerably  less,  of  course,  for  both 
villi  and  ridges  are  wanting.    Yet  even  here  considerable    absorp- 
tion takes  place.     When  the  mass  reaches  the  lower  end  of  the  in- 
testine, it  consists  of  little  but  the  indigestible  cellulose  of  vegetable 
foods,  some  undigested  connective  tissue,  waste  substances  from  the 
bile,  the  solids  in  the  mucous  secretion,  and  some  raw  starch  and 
undigested  fats  if  large  quantities  of  these  nutrients  have  been  eaten. 
This  refuse  of  the  food  is  thrown  off  from  the  body. 

VIII.  THE  LIVER  AND  ITS  FUNCTIONS 

142.  Position,  form,  size.  —  The  human  liver  (Fig.  26)  is  the  larg- 
est gland  of  the  body,  weighing  three  to  four  pounds.     It  lies  toward 
the  right  side  of  the  body,  just  beneath  the  diaphragm,  and  par- 
tially covers  the  pyloric  end  of  the  stomach.     It  consists  of  several 
lobes,  and  on  its  under  surface  there  is  a  small,  greenish  brown  sac 
called  the  gall  bladder.    The  deep  red  color  of  the  liver  is  partly  due 
to  the  fact  that  one  fourth  of  all  the  blood  of  the  body  is  found 
within  its  tissues. 

143.  Functions  of  the  liver.  —  The  liver  performs  three  important 
functions.     In  the  first  place,  it  secretes  a  golden    brown  liquid 
called  the  bile,  which  is  either  poured  at  once  through  the  bile  duct 
into  the  small  intestine  or  is  stored  in  the  gall  bladder  until  needed. 
If  the  bile  duct  becomes  stopped  up,  the  bile  is  absorbed  into  the 
blood  and  gives  to  the  tissues  the  yellow  tint  that  is  characteristic 


102  HUMAN  BIOLOGY 

of  jaundice.  The  liver,  in  the  second  place,  serves  as  a  great  store- 
house for  the  carbohydrates  when  the  blood  does  not  need  them  for 
immediate  use.  When,  on  the  other  hand,  there  is  a  lack  of  carbo- 
hydrates in  the  blood,  some  of  the  supply  in  the  liver  is  taken  up 
again  by  the  blood.  Finally,  the  liver  helps  to  destroy  some  of  the 
worn  out  cells  of  the  blood  (the  red  corpuscles),  and  the  waste 
materials  thus  formed  are  passed  off  into  the  intestine  as  a  part  of 
the  bile. 

IX.   HYGIENE  OF  DIGESTION 

144.  Hygienic  habits  of  eating.  —  One  should  form  the 
habit  of  eating  slowly  and  of  thoroughly  masticating  each 
mouthful  of  food.     For  by  this  process  the  food  is  thoroughly 
broken  up,  and  thus  is  prepared  for  rapid  digestion  not  only 
in  the  stomach  but  in  the  intestines  as  well.     The  process 
of  chewing  likewise  stimulates  the  flow  of  saliva.     Saliva 
not  only  helps  digest  food  in  the  mouth,  but  this  juice  also, 
when  swallowed  with  the  food,  continues  for  a  time  the  di- 
gestion of  starch  in  the  stomach  and  likewise  stimulates  to 
greater  activity  the  glands  in  the  walls  of  the  stomach. 

At  least  a  half  hour  should  be  devoted  to  the  eating  of 
dinner  and  twenty  minutes  to  breakfast,  lunch,  or  supper. 
The  proper  digestion  of  food  depends  in  no  small  degree  upon 
one's  mental  state;  worry  and  disagreeable  topics  should, 
therefore,  be  forgotten  as  far  as  possible  while  one  is  eating, 
and  the  mealtime  should  be  made  a  season  of  enjoyment. 
Regular  hours  of  eating  are  of  great  importance,  for  nothing 
more  commonly  deranges  the  digestive  system  than  the  con- 
tinual nibbling  of  food  or  sweetmeats  between  meals.  One 
should  refrain  from  vigorous  exercise  or  mental  exertion  for 
some  time  after  eating ;  the  reason  for  this  will  be  clear  after 
a  study  of  the  blood  system. 

145.  Prevention  of  disease.  —  To  insure  a  state  of  health 
the  useless  residue  of  the  food  should  be  expelled  from  the 


DIGESTION  AND  ABSORPTION  OF  NUTRIENTS     103 

large  intestine  regularly  each  day.  If  this  is  not  done, 
serious  disturbances  of  the  health  are  sure  to  follow.  By 
constipation  is  meant  the  abnormal  retention  of  waste  matter 
in  the  intestine.  "  The  causes  of  constipation  are  imperfect 
digestion  (due  to  deficient  secretion  in  the  alimentary  canal, 
inaction  of  the  liver,  or  insufficient  contraction  of  the  muscu- 
lar fibers  of  the  intestines),  insufficient  exercise,  the  use  of 
alcohol  or  drugs,  or  improper  food."  1 

Constipation  may  usually  be  counteracted  by  liberal  drink- 
ing  of  water,  especially  a  half  hour  before  breakfast,  and  by 
eating  food  with  laxative  effect,  —  for  example,  ripe  fruits 
(especially  figs),  green  vegetables  (especially  salads  with  oil), 
and  breads  made  of  the  coarser  graham  and  rye  flours. 

Dyspepsia,  also,  is  far  too  common,  and  is  one  of  the  most 
discouraging  diseases  to  treat,  because  it  shows  itself  in 
so  many  different  ways.  It  is  far  easier  to  prevent  than  to 
cure,  for  it  is  usually  caused  by  rapid  or  irregular  eating,  by 
taking  indigestible  foods,  by  lack  of  proper  exercise,  or  by 
worry ;  and  for  all  of  these  conditions  the  individual  is,  in  the 
main,  responsible. 

The  regulation  of  diet  in  time  of  sickness  is  a  most  impor- 
tant aid  to  recovery.  In  certain  diseases  it  is  necessary  that 
some  kinds  of  food  should  be  forbidden.  Whenever  the  func- 
tions of  the  body  are  not  carried  on  with  their  accustomed 
vigor,  the  physician  prescribes  foods  that  are  easily  digested 
-for  example,  milk,  raw  oysters,  toasted  bread,  and  soft- 
boiled  eggs. 

146.  The  use  of  water  as  a  drink.  —  "  Many  people,  and 
especially  many  women,  drink  too  little  water.  Water  is 
constantly  being  lost  through  the  lungs,  skin,  or  kidneys,  and 
this  loss  is  only  partially  made  good  by  the  oxidation  of  the 

1  From  New  International  Encyclopedia. 


104  HUMAN   BIOLOGY 

hydrogen  of  the  proteins  and  fats.  No  rules  as  to  the  amount 
can  be  given,  since  it  varies  so  much  with  temperature  and 
the  amount  of  muscular  activity ;  but  the  habit  of  drinking 
no  water  between  meals  and  but  little  at  the  table,  in  spite 
of  popular  opinion  on  the  subject,  is  to  be  deprecated.  .  .  . 

"  Undue  emphasis  has  been  laid  upon  the  danger  of  drink- 
ing water  with  meals.  The. reasons  given  —  that  such  water 
unduly  dilutes  the  gastric  juice  or  takes  the  place  of  a  normal 
secretion  of  saliva  —  are  questionable.  As  a  matter  of  fact, 
the  water  thus  taken  is  soon  discharged  into  the  intestine  and 
absorbed.  It  is  true,  however,  that  the  use  of  too  much 
fluid  with  the  meals  is  apt  to  lead  to  insufficient  mastication 
because  it  makes  it  easier  to  swallow  the  food;  and  from 
this  point  of  view  caution  is  advisable.  It  is  probably  also 
true  that  much  drinking  with  meals  tends  to  overeating, 
by  facilitating  rapid  eating."  —  HOUGH  and  SEDG WICK'S 
"  Human  Mechanism." 

147.  Effects  of  alcoholic  drinks  on  the  organs  of  diges- 
tion. —  Alcohol,  unlike  most  of  the  substances  taken  into 
the  alimentary  canal,  requires  no  digestion.  It  can,  there- 
fore, be  absorbed  very  rapidly  by  the  blood,  and  hence  alcohol 
is  possibly  sometimes  of  great  value  when  administered  by 
physicians,  in  cases  when  ordinary  food  cannot  be  digested. 
In  health,  however,  alcoholic  drinks  must  be  regarded  as  an 
expensive  and  extremely  dangerous  source  of  energy. 

According  to  the  best  authorities,  small  quantities  of 
alcohol  (when  sufficiently  diluted)  seem  for  an  adult  to 
stimulate  an  increased  flow  of  saliva  and  gastric  juice,  but 
even  this  is  doubtful.  The  time  required  for  the  digestion 
of  food,  when  alcohol  is  present  in  these  small  quantities, 
does  not  seem  to  be  increased.  Entirely  different  effects 
follow,  however,  when  strong  distilled  liquors  are  taken, 


DIGESTION   AND  ABSORPTION   OF  NUTRIENTS      105 


and  alcohol  in  any  large  quantity  often  produces  serious 
disturbances  of  the  organs  of  digestion.  This  is  especially 
true  when  liquors  are  taken  without  food ;  that  is,  between 
meals.  The  constant  danger  that  the  moderate  use  of  beer  and 
the  light  wines  will  lead  to  an  uncontrollable  thirst  for  alcohol 
cannot  be  emphasized  too  strongly.  All  authorities  agree,  too, 
that  the  growing  youth  should  let  alcohol  entirely  alone. 

148.    Review  of  Digestion 


REGION  OF  ALIMEN- 
TARY CANAL 

KIND  OF  SECRETION 
PRESENT 

PROCESSES  CARRIED  ON 

Mouth  cavity. 

Saliva    and 
mucus 

Mastication  of  food. 
Starch  changed  to  sugar. 
Sugar  and  salt  dissolved. 
Tasting    of    food    sub- 
stances. 
Small  amount  of  absorp- 
tion   of    water,    salt, 

sugar. 

Throat  cavity. 

Mucus. 

Passage  of  food  and  air. 

Gullet. 

Mucus. 

Passage  of  food  to  the 
stomach. 

106 


HUMAN  BIOLOGY 


REGION  OP  ALIMEN- 
TARY CANAL 

KIND  OP  SECRETION 
PRESENT 

PROCESSES  CARRIED  ON 

Stomach. 

Gastric     juice, 

Churning   of    food   by 

consisting  of 

the  muscles. 

water,     pep- 

Digestion of  starch  (by 

\ 

sin,  and   hy- 

saliva, for  short  time). 

drochloric 

Proteins  changed  to  pep- 

acid,    and 

tones. 

mucus. 

Insoluble  salts  changed 

to  soluble. 

Small  amount  of  absorp- 

tion of  water,   salts, 

sugars,  peptones. 

Small    intes- 

Pancreatic juice, 

Fats  changed  to  a  liquid 

tine. 

bile,  intestinal 

form  ready  for  absorp- 

juices   and 

tion. 

mucus. 

Starch  changed  to  sugar. 

Proteins     changed     to 

peptones. 

Large    amount    of    ab- 

sorption   of    fats    by 

lacteals  of  villi. 

Large    amount    of    ab- 

sorption of  water,  salt, 

sugar,    peptones,    by 

blood  vessels  of  villi. 

Large   intes- 

Mucus, and  in- 

Small   amount    of    ab- 

tine. 

testinal  juices 

sorption  of  nutrients. 

Removal    of    refuse    of 

food  from  the  body. 

CHAPTER  VI 
CIRCULATION    OF   THE   NUTRIENTS 

I.   COMPOSITION  OF  THE  BLOOD 

149.  Food    and    blood.  —  Thus    far    in    our    laboratory 
studies  we  have  tested  various  foods,  and  have  found  that 
they  all  consist  of  one  or  more  of  the  nutrients ;  namely, 
proteins,  fats,  carbohydrates  (i.e.  starch  and  sugar),  fats, 
mineral  matters,  and  water.     We  have  discussed  the  way 
in  which  each  of  these  nutrients  is  digested,  and  thus  made 
ready  for  absorption  into  the  blood  —  for  until  the  nutrients 
actually  become  a  part  of  blood,  they  cannot  be  of  use  to 
the  body.     In  7  we  described  the  red  and  white  corpuscles 
of  the  blood *  (Fig.  5)  and  there  stated  that  the  liquid  part  of 
blood  is  known  as  blood  plasma. 

150.  Composition  of  blood  plasma.  —  Blood  plasma  con- 
tains a  large  amount  of  water  in  which  are  dissolved  the 
various  nutrients  obtained  by  absorption  from  the  alimentary- 
canal .     The  presence  of   each  of   these  nutrients  has  been 
demonstrated  by  applying  the  various  food  tests  given  in 
23-28,    " Plant   Biology."     Following  is  the   percentage   of 
each  nutrient  found  in  the  human  body:  — 

Water 90+     per  cent 

Proteins 8+     per  cent 

Fats,  grape  sugar,  mineral  matters    ....    2"     per  cent 

1  For  a  laboratory  study  of  blood,  see  Peabody's  "  Laboratory 
Exercises,"  pp.  50-53. 

107 


108  HUMAN  BIOLOGY 

151.  Hygiene  of  the  plasma.  —  All  the  nutrition  of  the 
tissues  is  derived  from  the  blood,  and  all  the  nutrients  of  the 
blood  come  from  the  foods  we  eat.     If  these  foods  are  in- 
sufficient or  of  an  improper  kind,  the  blood  will,  of  course, 
be  deprived  of  necessary  ingredients,   and  the  cells  must 
inevitably  suffer  in  consequence.     Hunger  and  thirst  are 
the  sensations  that  tell  us  that  the  blood  is  in  need  of  new 
material.     That  this  is  true  is  demonstrated  by  the  fact  that 
these  sensations  disappear  when  water  and  liquid  food,  in- 
stead of  being  swallowed,  are  injected  directly  through  the 
skin  into  the  blood  vessels. 

152.  Blood  clotting.  —  When  blood  escapes  from  the  body, 
it  is  a  liquid  of  a  bright  red  color.     It  soon  changes  to  a  dark 
maroon,  however,  and  later  this  thickens  to  the  consistency 
of  jelly.     This  dark  red  mass  is  called  a  blood  clot,  and  the 
process  is  known  as  clotting  or  coagulation.     Coagulation  is 
of  great  practical  importance,  since  it  provides  a  natural 
means  of  closing  injured  blood  vessels,  and  of  preventing 
loss  of  blood. 

II.  CIRCULATION  AND  ITS  ORGANS 

153.  Necessity  for  the  circulation.  —  From  our  study  thus 
far,  we  have  found  that  our  bodies  are  composed  of  complex 
chemical  compounds  that  are  constantly  being  consumed 
in  the  development  of  heat  and  other  forms  of  energy.     It 
is  evident,  then,  that  every  organ  of  the  body,  and  indeed 
every  living  cell,  must  be  supplied  with  new  material  to  make 
good  these  losses  and  to  provide  for  growth.     The  source 
of  all  this  material  is  the  food  we  eat. 

In  the  last  chapter  we  considered  some  of  the  processes 
by  which  foods  are  converted  into  liquid  form  and  made  ready 
for  use  in  the  cells.  We  found  that  after  being  liquefied  these 


CIRCULATION  OF  THE  NUTRIENTS  109 

nutrients  are  absorbed  by  the  blood  vessels  in  the  walls  of 
the  alimentary  canal.  Since,  however,  many  tissues  of  the 
body  are  at  a  considerable  distance  from  the  organs  of  di- 
gestion, it  is  evident  that  some  means  must  be  provided  for 
supplying  each  cell  with  the  nutrients  it  needs.  This  is 
effected  by  the  circulation  of  the  blood.  By  the  term  cir- 
culation of  the  blood  is  meant  the  ceaseless  movement  of  the  blood 
through  a  system  of  tubes  called  blood  vessels. 

154.  Organs  of  circulation.  —  As  is  also  true  in  the  fish 
and  other  vertebrates,  the  force  that  drives  the  blood  around 
through  the  body  is  largely  furnished  by  the  contraction 
of  the  muscular  walls  of  the  heart.     Any  blood  vessel  that 
carries  blood  away  from  the  heart  is  called  an  artery.1     The 
veins  are  the  blood  vessels  that  bring  the  blood  back  to  the 
heart.     Connecting  the  arteries  and  the  veins  in  every  part 
of  the  body  are  countless  microscopic  blood  vessels  called 
capillaries  (Latin,  capillus  =  hair,  so  called  from  their  mi- 
nute size).     We  shall  now  consider  in  more  detail  the  struc- 
ture and  action  of  each  of  these  circulatory  organs. 

III.  THE  HEART 

155.  Position,    size,    shape.  —  The    heart    (Fig.  2)   is    a 
conical  or  pear-shaped  organ  about  the  size  of  the  fist.     It 
lies  behind  the  breastbone  near  the   middle   of  the   chest 
cavity,  with  its  pointed  end  or  apex  extending  toward  the 
left  side  between  the  fifth  and  sixth  ribs.     Since  the  beat  of 
the  heart  is  felt  most  plainly  near  the  apex,  it  is  commonly 
but  wrongly  believed  that  the  heart  lies  on  the  left  side  of 
the  body.     Let  one  imagine  the  front  wall  of  the  chest 

1  From  Greek,  aer  =  air  +  terein  =  to  hold  —  a  name  which  was 
given  by  the  early  anatomists  to  these  tubes,  because  they  were 
found  empty  after  death,  and  were  therefore  supposed  to  carry  air. 


110  HUMAN  BIOLOGY 

cavity  to  be  removed;  one  would  then  see  the  soft,  pink 
lungs  on  either  side,  nearly  filling  the  chest  cavity,  and 
between  them  the  heart  l  (Fig.  2). 

156.  Chambers  of  the  heart.  —  We  have  seen  (A.  B.,  99) 
that  a  fish's  heart  has  two  chambers,  an  auricle  to  receive 
the  blood  from  all  parts  of  the  body,  and  a  muscular  ventricle 
to  force  the  blood  into  the  arteries  which  carry  it  to  the  organs 
of  respiration  (gills)  and  thence  by  another  system  of  arteries 
to  all  parts  of  the  fish's  body.  In  the  human  circulatory 
system,  the  blood,  after  returning  to  the  heart  from  the  organs 
of  the  body,  is  likewise  forced  through  an  auricle,  a  ventricle, 
and  arteries,  and  so  reaches  the  breathing  organs  (lungs). 
Unlike  the  circulation  in  the  fish,  however,  the  blood  does 
not  pass  from  the  breathing  organs  to  the  other  parts  of  the 
body  directly,  but  returns  by  veins  to  the  heart,  and  so  an- 
other auricle  and  ventricle  are  provided  on  the  left  side  of 
the  heart.  These  receive  the  blood  from  the  organs  of 
respiration,  and  force  it  to  all  parts  of  the  body.  Thus  we 
see  that  we  have  two  hearts,  the  chambers  of  which  are 
completely  separated  by  a  muscular  partition;  the  right 
heart  receiving  the  blood  from  all  over  the  body  and  pump- 
ing it  to  the  lungs ;  the  left  heart  receiving  the  blood  from 
the  lungs  and  pumping  it  over  all  the  body. 

A  comparison  of  these  four  chambers  shows  important 
differences.  In  the  first  place,  the  auricles  have  relatively 
thin  walls  as  compared  with  the  ventricles,  and  the  reason 
for  this  is  evident  when  we  see  that  their  function  is  simply 
to  receive  the  blood  from  the  veins  and  to  push  it  downward 
into  the  ventricles.  When  one  compares  the  walls  of  the 

1  The  heart  is  not  only  surrounded  by  the  skeleton  and  muscles  of 
the  chest  wall,  but  it  is  also  inclosed  in  a  tough  bag  of  connective 
tissue  called  the  pericardium  (Greek,  peri  =  around  +  cardia  = 
heart). 


CIRCULATION  OF  THE  NUTRIENTS 


111 


left  ventricle  with  those  of  the  right,  one  is  struck  with  the 
great  thickness  of  the  former.  The  left  ventricle  does  much 
more  work  than  the  right ;  it  forces  blood  to  the  top  of  the 
head,  to  the  tips  of  the  fingers  and  toes,  and  to  every  other 
organ  of  the  body.  The  right  ventricle,  on  the  other  hand, 
pumps  blood  only  to  the  lungs  (Fig.  33): 


A  =  right  heart.  B  =  left  heart. 

FIG.  33.  — Cavities  of  heart. 

157.  Action  of  the  hoart.  —  The  blood  flows  into  the  right 
and  left  auricles  and  thence  into  the  corresponding  ventricles. 
When  the  ventricles  are  nearly  full  of  blood,  the  two  auricles 
contract  and  force  downward  enough  blood  to  fill  the  two 
ventricles  completely.  These  muscular  chambers  then  con- 
tract and  force  the  blood  out  into  the  arteries  that  lead  to 
the  lungs,  or  to  other  parts  of  the  body.  When  the  con- 
traction of  the  ventricles  takes  place,  it  is  evident  that  blood 
would  be  driven  back  into  the  auricles  were  there  not  some 
means  of  preventing  this  back  flow.  Hence,  between  each 


112  HUMAN  BIOLOGY 

auricle  and  ventricle  tough  flaps  of  membrane  are  provided 
which  close  the  opening  while  the  ventricles  are  contracting. 
Connected  with  each  of  these  flaps  are  tough  cords  of  tissue 
that  are  attached  to  the  muscular  walls  of  the  ventricle. 
These  cords  prevent  the  valves  from  being  forced  up  into  the 


A  =  positions  of  valves  before        B  =  position  of  valves  at  the 
the  contraction  of  the  ven-  beginning  of  the  contrac- 

tricle.  tion  of  the  ventricle. 

FIG.  34.  —  Diagrams  to  show  the  action  of  the  valves  of  the  heart. 

auricle  (Fig.  34) .  When  the  ventricles  cease  to  contract,  the 
blood  entering  the  auricles  presses  these  valves  downward 
and  so  enters  the  ventricles. 


IV.    THE  BLOOD  VESSELS 

158.  Position  of  arteries  and  the  pulse.  —  We  have  de- 
fined an  artery  as  a  blood  vessel  carrying  blood  from  the 
heart.  Every  time  the  ventricles  contract,  the  arteries 
leading  from  them  are  expanded,  and  this  is  true  of  every 
artery  in  the  body.  Most  arteries  lie  beneath  thick  layers 
of  muscle  or  bone,  which  protect  them  from  possible  injury; 
but  in  certain  regions  of  the  body  they  lie  close  to  the  sur- 
face. If  one  places  the  fingers  on  the  wrist  two  inches  or 
more  below  the  ball  of  the  thumb,  it  is  possible  to  feel  a 


CIRCULATION  OF  THE  NUTRIENTS 


113 


distinct  throbbing,  called  the  pulse.  This  is  due  to  the 
enlargement  of  the  artery  at  each  heart  beat  followed  by 
subsequent  contraction.  When  an  artery  is  cut,  therefore, 
the  blood  is  forced  out  in  spurts  at  each  contraction  of  the 
ventricle. 

159.  Structure  of  arteries.  —  If  a  piece  of  the  aorta  of 
any  animal  is  examined,  it  will  be  found  that  the  blood 
vessel  retains  its  tubular  form,  and  this  is  due  to  the  presence 


cells  of  lining 

membrane 


A  =  artery.  B  =  vein. 

FIG.  35.  —  Cross  section  of  blood  vessels. 


of  thick  layers  of  muscular  and  elastic  tissue  (Fig.  35). 
It  is  the  elastic  tissue  that  allows  the  arteries  to  expand 
when  more  blood  is  forced  into  them  by  the  contraction  of 
the  ventricles.  After  each  pulse  these  elastic  walls  squeeze 
the  blood  forward  into  the  capillaries;  arteries,  therefore, 
are  specially  adapted  to  keep  the  capillaries  full  of  blood. 

The  muscular  tissue  in  the  walls  of  the  arteries  aids  in 
regulating  the  size  of  the  arteries,  and  so  determines  the  rel- 
ative amount  of  blood  supplied  to  any  given  organ.  For 
example,  when  the  face  is  flushed,  the  muscles  in  the  arteries 
have  relaxed ;  pallor,  on  the  other  hand,  is  due  to  the  con- 
traction of  the  muscular  walls.  N 


114  HUMAN  BIOLOGY 

160.  A  study  of  the  pulse.  —  Laboratory  and  home  study. 

A.  To  take  the  pulse.     (Laboratory  study.) 

1.  Place  the  fingers  on  the  wrist  as  directed  in  158, 
and  count  the  pulse  while  sitting  quietly  for  a 
minute,  being  careful  not  to  miss  any  of  the  beats. 
Repeat  the  count  several  times,  until  the  numbers 
approximately  agree.  Describe  what  you  have 
done,  and  record  your  pulse  rate  in  your  note- 
book. 

2.  (Optional.)  In  a  table  like  the  following  record  the  number 
of  pupils  with  a  pulse  rate  (while  sitting  still)  correspond- 
ing to  the  headings  of  the  various  columns  named  below 
40-49  |  50-59  |  60-69  |  70-79  |  80-89  |  90-99  |  100+ 

B.  To  determine  the  effect  on  the  pulse  rate  of  different  posi- 

tions of  the  body.     (Home  work) . 

1.  Lie  a  few  moments  on  a  couch  and  completely  relax 

the  muscles.  Count  and  record  your  pulse,  re- 
peating the  count  till  the  number  during  a  minute 
is  reasonably  constant.  (It  is  better,  if  possible, 
to  have  some  one  else  do  the  counting.) 

2.  In  a  similar  way,  make  a  record  of  your  pulse  while 

sitting. 

3.  Determine,   likewise,   the  pulse  rate  when  you  are 

standing. 

4.  Take  some  vigorous  exercise  for  a  few  moments  (e.g. 

running  upstairs  or  riding  a  bicycle).1  Now  de- 
termine your  pulse  rate. 

5.  What  do  you  conclude,  therefore,  as  to  the  effect  on 

the  heart  beat  of  vigorous  muscular  activity?  In 
what  ways  may  the  rate  of  the  heart  beat  be  de- 
creased ? 

161.  Valves  at  the  mouth  of  arteries.  —  The  arteries  are 
always  full  of  blood,  and  when  the  ventricles  contract,  these 

1  In  case  the  pupil  has  any  heart  difficulty,  a  milder  form  of  exer- 
cise, such  as  walking  rapidly  or  swinging  the  arms,  should  be  taken. 


CIRCULATION  OF  THE  NUTRIENTS  115 

blood  vessels  have  to  be  stretched  in  order  to  accommodate 
the  additional  blood  that  is  forced  into  them.  Hence, 
when  the  ventricles  begin  to  relax,  the  blood  tends  to  rush 
back  into  these  chambers  from  the  arteries.  To  prevent 
this,  valves  are  placed  at  the  opening  of  each  of  the  two 
arteries  that  lead  from  the  right  and  left  hearts  (Fig.  33). 
Each  valve  is  shaped  like  a  watch  pocket.  The  three  open 
outward  from  the  heart,  but  as  soon  as  the  ventricles  begin 
to  relax,  the  blood  fills  up  the  pockets,  and  the  three  valves, 
by  meeting  in  the  middle  of  each  artery,  keep  the  blood  from 
returning  to  the  ventricles  (Fig.  33,  A). 

162.  Position  of  the  capillaries.  —  As  we  trace  the  arteries 
farther  and  farther  from  the  heart,  we  see  that  they  divide 
and  subdivide  until  very  small  branches  are  formed.     That 
these  fine  branches  are  still  arteries  is  proved  by  the  fact 
that  elastic  and  muscular  tissues  are  present  in  their  walls. 
Finally,  however,  these  tiny  blood  vessels  become  continuous 
with  still  smaller  tubes,  the  capillaries.     So  numerous  are 
the  capillaries  that  one  cannot  push  the  point  of  a  needle 
for  any  considerable  distance  into  any  organ  of  the  body 
without  piercing  a  number  of  them.     These  smallest  of 
blood  vessels   communicate  freely  with   one   another   and 
form  a  complicated  network  of  tubes  that  bring  blood  close 
to  all  cells  of  the  body. 

163.  Importance  of  the  capillaries.  —  If  the  blood  were 
kept  constantly  within  a  system  of  tubes  like  the  arteries, 
it  would  be  entirely  unable  to  help  in  the  nutrition  of  the 
body  because  osmosis  would  be  impossible.     Each  cell  of 
the  body  must  take  from  the  blood  the  nutrients  it  needs 
for  its  special  work;   likewise  it  must  give  off  to  the  blood 
the  wastes  it  has  formed  by  oxidation.     It  is  through  the 
thin-walled  capillaries  that  all  these  exchanges  of  materials 


116 


HUMAN  BIOLOGY 


.4  =  Surface  view.    B= Longitudinal  section. 
FIG.  36.  —  Structure  of  capillaries. 


occur.     Hence,   the   capillaries   form   the   most   important 
portion  of  the  blood  system. 

164.  Structure  of  the  capillaries.  —  In  structure  the  capil- 
laries are  extremely  simple  (Fig.  36).     At  the  points  in  the 

blood  system  where  arteries 
end  and  capillaries  begin, 
muscular  and  elastic  tissues 
are  wanting.  The  walls  of 
the  capillaries  are  formed  of 
a  single  layer  of  very  thin- 
walled  cells.  We  have  in 
this  arrangement  the  best 
possible  conditions  for  the 
process  of  osmosis.  Only 
the  thin  membrane  of  the 
capillary  wall  separates  the 

blood  from  the  surrounding  tissues,  and  an   exchange  of 
materials  between  the  two  is  readily  carried  on. 

165.  Position  of  the  veins. 
—  On  the  back  of  the  hand  one 
sees  through  the  skin  a  branch- 
ing system  of  bluish  blood  ves- 
sels.   These  are  veins.    Unlike 
the    arteries,    veins    have    no 
pulse.     Many  veins,  like  those 
in  the  hand,  lie  near  the  sur- 
face, while  most  of  the  arteries, 

as  we  have  stated  above,  are     f  =  vein  laid  open  to  show  shape  of 

valves ;  B  =  section  of  vein  showing  valve 

buried  deeply  among  the  Other    open ;  C  =  section  of  vein  showing  valve 
,.  closing. 

tissues. 

166.  Structure  of  veins.  —  When  the  veins  are  emptied 
of  blood,  they  immediately  collapse.     This  is  due  to  the  fact 


A  DC 

FIG.  37. — Structure  of  a  vein. 


CIRCULATION  OF  THE  NUTRIENTS  117 

that  their  walls  have  far  less  muscular  and  elastic  tissue  than 
have  the  walls  of  arteries.  Veins,  however,  are  provided  with 
valves  shaped  much  like  the  valves  at  the  mouth  of  the  large 
arteries  leading  from  the  heart.  The  blood  can  flow  toward 
the  heart,  but  as  soon  as  it  begins  to  pass  in  the  opposite 
direction,  these  valves  are  immediately  filled  and  thus  the 
passage  is  obstructed  (Fig.  37). 

V.  CIRCULATION  OF  THE  BLOOD 

167.  Course  of  the  blood  through  the  body.  —  Having 
completed  our  survey  of  'the  structure  and  action  of  the  heart 
and  the  blood  vessels,  we  are  ready  to  study  the  blood  system 
as  a  whole  and  to  learn  how  the  blood  goes  to,  through,  and 
from,  the  organs  of  the  body.  Let  us  now  follow  the  course 
of  the  blood  from  the  time  it  leaves  the  left  ventricle  until 
it  again  returns  to  this  chamber  of  the  heart.  When  the 
left  ventricle  contracts,  the  blood  is  forced  out  into  the  largest 
artery  of  the  body,  which  is  known  as  the  aorta.  This  blood 
vessel  forms  an  arch  (Fig.  38)  from  the  upper  portion  of 
which  branches  extend  to  the  head  and  the  arms.  The  aorta 
then  continues  downward  through  the  chest  and  abdominal 
cavities,  supplying  on  its  way  the  various  organs  in  these 
regions.  It  then  divides  into  two  arteries  that  continue  down 
the  legs.  Each  of  these  larger  arteries  that  we  have  men- 
tioned divides  again  and  again,  until  finally  the  blood  is  forced 
through  a  network  of  very  fine  capillaries  in  the  various 
organs  to  which  the  arteries  extend. 

From  these  capillaries  blood  passes  into  tiny  veins  which 
carry  all  the  blood  into  two  large  veins,  one  from  the 
upper  part  of  the  body,  the  other  from  the  lower  part  of 
the  body ;  and  these  two  veins  finally  empty  into  the  right 
auricle  of  the  heart.  Thence  the  blood  passes  into  the  right 
ventricle. 


118 


HUMAN  BIOLOGY 


4rcnofaorta\  - 


/?/gfrt  ventr/c/e .... 
Abdo/n/na/aorta—.. 


/nfer/'or  vena  cava  -L 


Ve/ns  from-  ..... 
kidneys 


£ranc/?es  of-  -'' ' ' 
aorta  M  /ntest/nes 

£rcr/?c/?es  of-"" 
aorta  to  /eg-s 


Ye/ns from heart 

'/''  f , ,  'Arteries  fa  head 
Me//?  fro/r?  arm 

Artery  to  arm 

~  -  ~rhorac/c  aorta 
—-Stomach 

-  -  -branch  ofaorta  to 
stomach.s/3/eer? 


'-Sp/eer? 

-  -  -ffcrtf/c*/ artery 

•--U/nar  artery 


Branches  of  aorta 
to  Aiafneys 


— Artery to  /e$ 
—-  j/e/nfrom  lea 


FIG.  38. — Diagram  of  the  circulation  to  and  from  the  various  organs  of  the 
body  except  the  lungs. 


CIECULATION  OF  THE  NUTRIENTS 


119 


The  right  ventricle  by  its  contraction  drives  the  blood 
through  an  artery  to  each  of  the  lungs,  until  it  finally  reaches 
the  countless  capillaries  in  the  interior  of  these  organs.  Veins 
now  receive  this  blood  and  convey  it  to  the  left  auricle, 
whence  it  again  enters  the  left  ventricle.  About  one  half 
minute  is  required  to  complete  the  circulation. 

168.  Changes  in  the  composition  of  the  blood.  —  The 
composition  of  the  blood  is  continually  changing  in  its  pas- 
sage through  the  various  tissues  of  the  body.  We  may, 
perhaps,  make  clearer  these  various  changes  by  expressing 
them  in  tabular  form  as  follows :  — 


BLOOD  LOSES 

BLOOD  GAINS 

In  muscles,  nerves, 

Materials  needed 

Wastes  formed  by 

and  other 

for    growth,    re- 

oxidation (carbon 

tissues. 

pair,  and  produc- 

dixoid, water, 

tion  of  energy. 

and  other  wastes)  . 

In  lining  of  mouth, 

Materials  needed 

Digested  nutrients. 

stomach, 

for  the  manufac- 

intestines. 

ture  of  digestive 

juices      and    for 

growth    and    re- 

i 

pair. 

In  lungs. 

Carbon  dioxid  and 

Oxygen. 

water. 

In    kidneys    and 

Water    and    other 

Carbon  dioxid. 

skin. 

wastes. 

VI.   HYGIENE  OF  THE  CIRCULATION 

169.  Effect  of  exercise  on  the  heart.  —  The  pulse  rate 
is  slowest  when  we  are  asleep.  As  the  activities  of  the  day 
begin,  the  heart  beat  is  quickened,  and  after  violent  exercise 


120  HUMAN  BIOLOGY 

this  organ  may  beat  as  often  as  twice  a  second.  Exercise, 
when  properly  regulated,  is  undoubtedly  beneficial  to  every 
organ  of  the  body,  for  the  heart  should  be  kept  in  such  a 
vigorous  condition  that  it  is  ready  to  meet  not  only  the  ordi- 
nary requirements  of  everyday  life,  but  even  the  strain  that 
may  come  in  such  emergencies  as  necessary  escape  from 
danger  or  recovery  from  disease. 

It  is  easily  possible,  however,  to  overstrain  the  heart 
muscle  by  exacting  from  this  organ  too  violent  or  too  pro- 
longed activity  (e.g.  in  sprinting  or  in  long  distance  runs  and 
bicycle  rides).  These  often  result  in  permanent  thickening 
of  the  walls  of  the  valves  of  the  heart.  Before  a  youth  takes 
part  in  athletic  contests,  he  should  consult  a  competent 
physician  as  to  the  wisdom  of  his  taking  violent  exercise. 

170.  Effect   of   exercise   on   the   blood   vessels.  —  When 
one  is  using  the  muscles  actively,  greater  oxidation  of  the 
tissues  goes  on,  and  a  larger  amount  of  blood  is  needed   to 
supply  the  oxygen  and  to  remove  the  added  wastes  formed 
by  this  increased   oxidation.     The  muscular  walls  of  the 
arteries  relax  in  the  organs  that  are  specially  active,  thus 
supplying  these  organs  with  more  blood.     It  is  manifestly 
impossible  to  have  an  increased  supply  of  blood  in  the  organs 
of  digestion,  in  the  muscles,  and  in  the  brain  all  at  the  same 
time.     This  is  the  reason  why  it  is  unhygienic  for  an  adult 
to  exercise  violently  or  to  carry  on  any  considerable  degree 
of  mental  activity  immediately  after  a  hearty  meal.     Per- 
sistence in  violating  this  rule  usually  results  in  attacks  of 
indigestion. 

171.  Stopping  of  blood    flow  in  wounds.  —  One  can  tell 
when  an  artery  has  been  cut  by  the  fact  that  blood  comes 
out  in  spurts.     Since  the  blood  is  on  its  way  from  the  heart, 
the  flow  can  be  stopped  or  lessened  in  this  kind  of  accident 


CIRCULATION  OF  THE  NUTRIENTS  121 

by  applying  pressure  on  the  side  of  the  wound  nearest  the  heart.1 
Thus  if  the  finger  is  cut  deeply  and  the  blood  jets  forth,  a 
strong  cord  or  a  handkerchief  should  be  tied  loosely  about 
the  wrist,  a  wad  of  paper,  or  a  pebble  being  placed  directly 
beneath  the  knot  and  over  the  artery.  A  pencil  or  piece 
of  wood  should  then  be  run  through  the  loop,  and  the  knot 
should  be  twisted  until  the  blood  flow  is  stopped  by  the  pres- 
sure. When  blood  flows  evenly  from  a  wound,  it  is  an  in- 
dication that  a  vein  has  been  cut,  and  the  pressure  should 
be  applied  in  a  similar  way  on  the  side  away  from  the  heart. 
If  unable  to  decide  whether  an  artery  or  a  vein  has  been 
cut,  put  the  bandage  directly  over  the  cut.2 

Bleeding  from  the  nose  may  usually  be  stopped  by  holding 
the  head  erect,  and  by  applying  cold  water  to  the  bridge  of 
the  nose  or  to  the  back  of  the  neck. 

1  Every  pupil  should  practice  the  method  of  applying  a  bandage 
in  accordance  with  the  directions  given  in  this  section. 

2  For  further  treatment  of  cuts  and  bruises  see  25. 


CHAPTER  VII 

RESPIRATION  AND   THE  PRODUCTION   OF  ENERGY  IN 

MAN 

I.  NECESSITY  FOR  RESPIRATION 

172.  To  prove  that  oxidation  takes  place  in  the  human 
body.1  —  Laboratory  study. 

A .  Development  of  heat  in  the  human  body. 

Secure  two  chemical  thermometers  that  approximately 
agree  at  the  room  temperature.  Support  one  of  the  ther- 
mometers so  that  it  hangs  free  in  the  air ;  clasp  the  bulb  of 
the  other  thermometer  in  the  palm  of  the  hand  for  several 
minutes. 

1.  Describe  the  experiment  as  it  was  performed. 

2.  Note  and  record  the  temperature  as  indicated  on  each 

of  the  thermometers. 

3.  What  evidence  have  you  that  heat  is  produced  in  the 

human  body  ? 

B.  Production  of  carbon  dioxid  in  the  human  body. 

Blow  the  breath  through  a  tube  into  a  bottle  or  test 
tube  of  lime  water. 

1.  Describe  what  was  done. 

2.  What  proof  have  you  that  carbon  dioxid  is  given  off 

from  the  body? 

3.  What  element  found  in  foods  and  protoplasm  must 

be  oxidized  in  order  to  produce  carbon  dioxid? 

1  The  student  should  review  P.  B.,  75  (to  prove  that  heat  energy 
is  developed  in  growing  seedlings)  and  P.  B.,  81  (to  prove  that  car- 
bon dioxid  is  formed  during  the  growth  of  seedlings). 

122 


RESPIRATION  AND  ENERGY  IN  MAN  123 

4.  State  now  two  evidences  that  oxidation  is  carried  on 

in  the  human  body. 

5.  What  element  must  always  be  present  in  order  that 

oxidation  may  be  carried  on? 

173.  Examples  of  energy  in  the  human  body.  —  While 
studying  plants,  we  enumerated  various  ways  hi  which  these 
living   organisms   exhibit   the    energy   which   is   developed 
within    them    (P.   B.,  74),    and    we    have    likewise    called 
attention  to  evidences  of  energy  in  animals.     In  human 
beings  the  forms  of  energy  are  much  more  varied  and  strik- 
ing.    For  example,  the  movements  of  each  of  the  five  hun- 
dred separate  muscles  found  in  the  body  are  all  due  to  the 
muscular  energy  developed  in  their  protoplasm;   the  control 
of  all  these  muscles  is  due  to  energy  liberated  in  the  nervous 
system  (nervous  energy) ;    all  the  glands  that  produce  the 
varied  ferments  owe  their  ability  to  do  their  work  to  the 
release  of  chemical  energy;  and  when  we  come  to  deal  with 
the  highest  functions,  namely,  feeling,  thinking,  and  willing, 
it  seems  probable  that  all  of  them  are  made  possible  by 
the  setting  free  of  some  form  of  energy.     In   connection 
with  the  development  of  all  these  forms  of  energy,  heat 
energy,  as  we  proved  in  172,  is  liberated. 

174.  Transformations  of  energy.  —  While  considering  the 
functions  of  green  plants  we  found  that  the  energy  of  the  sun 
is  utilized  and  stored  in  the  manufacture  of  food  materials, 
and  thus  is  made  available  for  the  use  of  the  plant.     Con- 
sequently, when  we  take  into  our  bodies  and  digest  the  various 
nutrients  produced  by  green  plants,  these  food  substances 
become  available  as  our  sources  of  energy.     But  to  release 
this  stored-up  energy,  whether  in  muscle,  gland,  or  nerve 
cells,  oxygen  is  always  essential.     Hence,  a  constant  supply 
of  oxygen  for  the  body  is  necessary.     When  this  oxygen 


124  HUMAN  BIOLOGY 

combines,  in  the  process  of  oxidation,  with  the  carbon, 
hydrogen,  and  other  elements  in  the  foods  or  protoplasm, 
waste  matters  (carbon  dioxid,  water,  etc.)  are  produced,  and 
for  the  healthy  working  of  the  body,  these  wastes  must  be 
eliminated.  We  are  now  to  see  how  the  body  is  adapted 
to  secure  an  adequate  supply  of  oxygen  and  to  rid  itself 
of  harmful  waste  matters. 

175.  Respiration  in  plants,  animals,  and  man.  —  It  should 
be  clear  from  our  study  thus  far  that  all  living  things  require 
oxygen,  and  that  this  oxygen  brings  about  in  plants,  animals, 
and  man  a  process  resembling  oxidation,  at  least  in  the  re- 
leasing of  heat  and  of  other  forms  of  energy,  and  in  the  pro- 
duction of  carbon  dioxid  and  other  waste  matters.     These 
various  processes  doubtless  take  place  in  each  living  cell. 
Hence,  every  cell  must  be  supplied  with  oxygen  and  must 
necessarily  form  carbon  dioxid.     The  process  by  which  plants 
or  animals  take  in  oxygen  and  get  rid  of  carbon  dioxid  is  known 
as  breathing.     And  when  we  include  also  the  oxidation  that 
takes  place  within  the  cells  and  the  elimination  of  the  wastes 
from  the  cells,  this  whole  series  of  processes  is  known  as 
respiration. 

Breathing  involves  two  distinct  processes ;  first,  that  of 
taking  into  the  lungs  new  supplies  of  fresh  air,  and  secondly, 
that  of  removing  from  the  lungs  the  impure  air  that  has  been 
used.  To  the  first  process  is  given  the  name  inspiration 
(Latin,  in  =  into  +  spirare  =  to  breathe) ;  the  second  is  called 
expiration  (Latin,  ex  =  out  +  spirare  =  to  breathe). 

II.  ADAPTATIONS  FOR  SECURING  OXYGEN  AND  FOR 
EXCRETING  CARBON  DIOXID 

176.  Course  taken  by  the  air.  —  In  ordinary  breathing, 
air  enters  the  body  through  the  two  nostrils  (the  left  one  is 


RESPIRATION  AND  ENERGY  IN  MAN 


125 


shown  in  Fig.  39),  and  then  through  the  two  nasal  passages 
it  enters  the  throat  cavity.  In  the  lower  region  of  the  throat 
is  the  slit-like  glottis  opening, 
through  which  the  air  enters 
the  larynx  or  voice  box.  The 
latter,  commonly  known  as 
" Adam's  apple,"  projects  some- 
what on  the  front  of  the  neck. 
Below  the  larynx  is  the  contin- 
uation of  the  windpipe,  which, 
just  above  the  level  of  the  heart, 
divides  into  two  main  branches 
(Fig.  40) ,  one  of  which  supplies 
air  to  the  right  lung,  the  other 
to  the  left  lung.  Within  the 
lungs  these  tubes  branch  off 
into  a  vast  number  of  very 
small  pipes,  called  bronchial 
tubes.  The  finest  divisions  of 
these  tubes  open  into  extremely 
thin-walled  air  sacs  (Fig.  41). 

177.     The  nose  cavity.  —  The     FlG-  39.  —  Longitudinal  section  of 

head  and  neck  showing  food  and 

openings  into  the  nasal  passages      air  passages, 
are  guarded  by  a  mass  of  pro- 
jecting hairs,  by  means  of  which 
a  considerable  amount  of  dust 
is  kept  from  entering  the  lungs. 
The  nose  itself  is  lined  by  mu- 
cous membrane  which   covers 
the  whole  interior  of  the  nasal 
chambers.     Its  mucous  secretion  collects  most  of  the  dirt 
and  germs  that  have  passed  the  hairs  in  the  nostrils. 


a  =  vertebral  column. 

b  =  gullet. 

c  =  windpipe. 

d  =  larynx. 

e  =  epiglottis. 

/  =  uvula. 

g  =  opening  of  left  Eustachian  tube. 

h  =  opening  to  tear  duct. 

k  =  tongue. 

I  =  hard  palate. 


126 


HUMAN  BIOLOGY 


178.    The  throat  and  larynx.  —  Except  when  something 

is  being  swallowed,  the 
glottis  is  always  open, 
thus  allowing  a  free 
passage  for  the  air  from 
the  throat,  through  the 
larynx,  into  the  wind- 
pipe. When  food  is 
swallowed,  it  is  of 
course  important  that 
the  windpipe  be  closed, 
and  this  is  accom- 
plished by  a  little  trap- 
door called  the  epiglottis 
(Fig.  39).  If  one  puts 
the  finger  on  the  larynx 
region  and  then  swal- 


FIG.  40.  —  Windpipe  and  lungs. 


lows,  one  can  feel  this 
organ  rising  to  meet  the 
epiglottis.  Within  the  voice  box  are  two  thin  membranes 
that  may  be  stretched  "with  more  or  less 
tension  and  set  in  vibration  by  the  in- 
spired or  expired  air.  These  vocal  cords 
help  to  produce  the  various  tones  of  the 
voice. 


179.    Lining  of  the  air  passages.  — The 

mucous  lining  of  the  nasal  cavities  and  of 
the  windpipe  and  its  branches  is  especially 
interesting.  The  cells  that  cover  these 
passageways  are  covered  by  minute  hair- 
like  projections  called  cilia,  much  like  those  on  the  outside 
of  a  paramecium  (A.  B.,  120),  which  wave  upward  toward 


FIG.  41.  —  Two  air  sacs 
with  their  branches. 


RESPIRATION  AND  ENERGY  IN  MAN  127 

the  throat  with  a  quick  movement,  and  then  more  slowly 
recover  their  former  position  (Fig.  18) .  In  this  way  any  dust 
particles  that  have  passed  the  barrier  of  hairs  at  the  nostril 
openings  and  the  mucus  secreted  by  the  membrane  are 
moved  steadily  upward  until  they  reach  a  point  where  they 
can  be  coughed  out  into  the  mouth  cavity. 

180.  The  lungs.1  —  When    the    finest    branches   of    the 
bronchial  tubes  are  traced,  we  find  that  each  one  ends  in 
a   branching  air  sac  with  extremely  thin  walls   of  elastic 
tissue  (Fig.  41).     When  air  comes  into  these  sacs,  they  are 
expanded;    but   as   expiration   begins,    their    elastic    walls 
help  to  force  back  through  the  branches  of  the  windpipe  the 
air  that  has  been  taken  into  the  lungs. 

181.  Blood  supply  to  the  lungs.  —  The  artery  supplying 
the    lungs,    as    we    learned    (167),    arises    from    the    right 
ventricle  and  soon  divides  into  two  branches,  one  for  the 
right  and  one  for  the  left  lung.     Within  the  lung  tissue  each 
artery  divides  into  small  branches  that  follow  the  course  of 
the  bronchial  tubes  to  the  air  sacs.     Here  the  arteries  com- 
municate with  a  maze  of  capillaries  that  run  just  beneath 
the  thin  lining  of  the  air  sacs.     It  is  here  that  the  exchange 
of  material  takes  place  between  the  blood  and  the  inhaled 
air,  for  the  two  are  separated  only  by  the  extremely  thin 

1  One  can  get  a  good  idea  of  the  structure  of  the  human  air 
passages  and  lungs  by  securing  from  the  butcher  the  chest  organs 
of  a  sheep  or  calf.  These  consist  of  the  larynx,  windpipe,  and  its 
branches,  and  the  two  lungs,  between  which  lies  the  heart.  A  piece 
of  the  diaphragm  should  also  be  secured  if  possible.  The  lungs 
are  composed  of  soft,  pink  tissue,  easily  compressed  by  the  hands. 
If  air  is  forced  through  a  tube  inserted  in  the  glottis  opening,  the 
lungs  swell,  and  when  fully  distended  occupy  a  space  several  times 
their  size  when  collapsed.  Just  as  soon  as  one  ceases  to  blow  into 
the  lungs,  these  organs  begin  to  collapse,  and  soon  reach  their 
former  condition.  The  characteristics  of  the  lungs  and  air  pas- 
sages should  be  demonstrated  before  180  is  assigned  for  study. 


128  HUMAN  BIOLOGY 

walls  of  the  air  sacs  and  of  the  capillaries.  From  the  capil- 
laries of  the  lungs,  the  blood  finally  collects  into  veins  that 
convey  the  blood  to  the  left  auricle. 

182.  The  function  of    red  corpuscles.  —  In  7  we  called 
attention  to  the  structure  of  the  red  corpuscles  of  the  blood. 
Like  other  cells  red  corpuscles  are  composed  of  protoplasm. 
Chemical  analysis  shows  that  the  most  important  ingredient 
is  a  protein  substance  called  hemoglobin,  a  compound  that 
contains  iron.     Hemoglobin  gives  the  red  color  to  the  blood 
and  has  a  remarkable  power  of  combining  with  oxygen  when 
that  element  is  abundant,  and  of  giving  it  up  wherever  it  is 
needed  in  the  various  parts  of  the  body.     We  may,  therefore, 
compare  the  blood  corpuscles  to  countless  little  boats,  float- 
ing in  a  stream  of  plasma ;  they  take  on  their  cargo  of  oxygen 
from  the  air  in  the  lungs  and  discharge  it  in  the  cells  of  the 
tissues. 

183.  Change  in  the  color  of   the  blood  after  mixing  with 
oxygen.  —  When  the  blood  passes  through  the  lungs,   as 
already  stated,  it  absorbs  oxygen.     The  resulting  change 
in  color  is  seen  from  the  following  experiment.     Pour  into  a 
glass  bottle  a  small  amount  of  blood  that  has  been  prevented 
from  clotting  by  stirring  it  vigorously  with   a  bunch  of 
twigs,  and   stopper  tightly.     When    the    bottle  is  shaken 
violently,  the  blood  is  mixed  with  the  oxygen  in  the  bottle, 
and  the  dark  maroon  color  changes  almost  instantly  to  a 
bright  scarlet.     The  pupil  will  doubtless  have  observed  that 
the  blood  in  the  veins  on  the  back  of  the  hand,  for  instance, 
is  blue,  but  that  whenever  blood  flows  from  any  of  these 
veins  because  of  a  slight  cut,  the  color  is  always  bright  red 
after  the  blood  comes  in  contact  with  the  oxygen  of  the  air. 

184.  Hygiene   of    the  red   corpuscles.  —  Since  supplying 
oxygen  to  the  various  tissues  is  the  function  of  the  red  cor- 


RESPIRATION  AND  ENERGY  IN  MAN  129 

puscles,  it  is  very  important  that  their  number  be  sufficient 
and  that  they  be  kept  in  a  healthy  condition.  To  this  end, 
an  abundance  of  sleep,  exercise,  fresh  air,  and  nutritious  foods 
are  the  essential  conditions.  Every  one  is  familiar  with  the 
fact  that  the  face  looks  pale  after  loss  of  sleep,  or  when  food 
and  fresh  air  are  insufficient,  or  during  periods  of  physical 
inactivity,  and  this  appearance  indicates  a  lack  of  red  cor- 
puscles. Habitual  paleness,  or  a-nce'mi-a,  is  a  disease  re- 
quiring medical  treatment.  It  is  frequently  due  to  a  want 
of  iron  in  the  system ;  hence,  the  value  of  spinach  and  other 
vegetable  foods  containing  this  element.  Fresh  air,  a  mod- 
erate amount  of  exercise,  and  good  food  are  usually  the 
best  remedies  for  anaemia.  A  good  complexion  is,  therefore, 
very  largely  dependent  on  healthy  blood.  Paint,  powder, 
and  other  cosmetics  will  not  give  such  a  complexion;  and 
besides  cheapening  the  individual  who  uses  them  habitually, 
they  are  often  a  source  of  permanent  injury  to  the  skin  and 
blood. 

III.   THE  PROCESS  OF  BREATHING 

185.  Structure  of  the  chest  cavity.  —  In  the  upper  portion 
of  the  trunk  is  the  cone-shaped  chest  cavity,  which  is  more 
or  less  inclosed  by  the  breastbone,  the  ribs,  the  collar  bones, 
and  the  spinal  column.     This  bony  framework  is  covered  by 
muscles  that  help  to  move  the  ribs,  and  by  the  outside  cover- 
ing of  skin.     The  floor  of  the  chest  cavity  is  formed  by 
the  tough  sheet  of  muscle  and  connective  tissue,  the  dia- 
phragm.    In  this  way  there  is  formed  an  air-tight  compart- 
ment, which  is  completely  filled  by   the  heart,  the  blood 
vessels,  the  gullet,  and  the  lungs  (Figs.  1  and  2). 

186.  The  pleura.  —  The  outer  surface  of  each  lung  is  covered 
with  a  thin  layer  of  membrane,  and  the  walls  of  the  chest  cavity 
are  lined  with  the  same  kind  of  tissue.     These  two  layers  constitute 


130  HUMAN  BIOLOGY 

the  pleura.    Both  surfaces  secrete  a  liquid  which  enables  the  lungs 
to  glide  over  the  chest  wall  without  friction. 

187.  To  determine   the    amount  of    enlargement  of    the 
chest  cavity  during  inspiration.  —  (Home  work.) 

Force  the  air  out  of  the  lungs  as  completely  as  possible. 
Draw  a  tape  or  cord  around  the  chest  under  the  armpits, 
keeping  it  reasonably  tight,  and  thus  measure  the  girth  of 
the  chest. 

1.  State  what  you  have  done,  and  record  in  inches  the  meas- 

urement thus  determined. 

2.  Inhale  as  much  air  as  possible,  and  again  record  the  chest 

measurement  as  directed  above. 

3.  State  the  difference  in  the  measurements  thus  obtained. 

4.  What  is  your  conclusion,  therefore,  as  to  the  amount  of 

enlargement  of  the  chest  cavity  ? 

188.  How  air  is  taken  into  the  lungs.  —  The  chest  cavity 
is  not  like  most  boxes  inclosed  by  rigid,  immovable  walls, 
for  it  may  be  enlarged  in  its  three  dimensions ;  namely,  from 
side  to  side,  from  front  to  back,  and  from  top  to  bottom. 
We  shall  now  consider  how  this  is  made  possible.     A  study 
of  the  skeleton  will  show  that  the  ribs  are  joined  to  the  verte- 
brae in  the  back  of  the  chest  region  and  to  the  breastbone 
in  front  in  such  a  way  that  it  is  possible  to  raise  and  lower  the 
front  ends.     When  the  air  is  forced  out  of  the  chest  cavity, 
the  front  ends  of  the  ribs  are  lowered  and  so  the  breastbone 
is  pulled  nearer  to  the  spinal  column.     As  we  inspire,  the 
muscles  that  run  from  the  upper  part  of  the  trunk  to  each 
xof  the  ribs  contract,  and  so  these  bones  are  pulled  upward 
toward  a  horizontal  position.     By  this  movement  the  breast- 
bone is  pushed  farther  away  from  the  spinal  column,  and  the 
ribs  themselves  press  outward  at  the  sides.     In  this  way  the 
capacity  of  the  chest  cavity  is  increased  from  side  to  side, 
and  from  front  to  back. 


RESPIRATION  AND  ENERGY  IN  MAN  131 

When  the  diaphragm  is  at  rest,  it  forms  a  dome-shaped  par- 
tition between  the  organs  of  the  chest  and  those  of  the  abdo- 
men (Fig.  42).  During  inspiration,  the  muscles  of  which 
the  diaphragm  is  largely  composed,  are  made  to  contract, 
the  dome  of  this  organ  becomes  flattened,  and  so  presses 
down  upon  the  stomach,  liver,  and  other  abdominal  organs, 
and  these  in  turn  force  outward  the  wall  of  the  abdomen. 
By  the  action  just  described,  the  size  of  the  chest  cavity 
is  increased  in  its  third  dimension;  namely,  from  top  to 
bottom. 

Thus,  by  the  combined  movements  of  the  ribs  and  dia- 
phragm, the  chest  cavity  is  enlarged  hi  all  three  of  its  dimen- 
sions. The  walls  of  the  chest  cavity  would,  therefore,  tend  to 
move  away  from  the  lungs ;  but  the  air  already  in  the  lungs 
expands  the  many  air  sacs  in  the  lung  tissue,  and  so  keeps  these 
organs  in  close  contact  with  the  chest  walls.  The  moment, 
however,  that  the  air  sacs  begin  to  enlarge,  the  air  expands 
to  fill  the  larger  space,  and  so  the  pressure  of  the  air  on  every 
square  inch  inside  the  lungs  is  diminished,  and  therefore 
becomes  less  than  the  air  pressure  outside  the  body.  At 
once  more  air  is  forced  in  through  the  air  passages  until  the 
pressure  within  and  outside  the  body  becomes  equalized. 
This  process  we  have  described  is  called  inspiration.  Every 
inspiration  requires  muscular  action  in  elevating  the  ribs  and 
flattening  the  diaphragm. 

189.  To  determine  the  breathing  capacity  of  the  lungs.  — 
Laboratory  demonstration. 

Fill  a  large  tray  half  full  of  water.  Mark  on  a  gallon  bottle 
the  level  of  1,2,  3,  and  4  quarts ;  completely  fill  the  bottle 
with  water,  and  invert  it  in  the  tray,  just  as  was  done  in 
collecting  oxygen  and  other  gases  (P.  B.,  10).  Beneath 
the  mouth  of  the  bottle  insert  one  end  of  a  glass  or  rubber 
tube.  Now  take  in  a  deep  inspiration,  filling  all  parts  of  the 


132  HUMAN  BIOLOGY 

lungs  as  completely  as  possible,  then  slowly  exhale,  blowing 
the  breath  through  the  tube.  Make  sure  that  only  one 
complete  expiration  is  carried  on,  and  take  care  that  all  the 
expired  air  is  collected  in  the  bottle. 

1.  Describe  the  way  the  experiment  was  carried  on. 

2.  Note  the  number  of  quarts  occupied  by  the  expired  air 

in  the  bottle,  and  record  this  in  your  notebook. 

3.  What  do  you  conclude,  therefore,  as  to  the  amount  of  air 

that  may  be  forced  out  of  the  two  lungs  of  the  individual 
who  performed  the  experiment? 

4.  (Optional.)    Ask  the  pupil  who  has  the  highest  record  of  differ- 

ence in  chest  measurement  before  and  after  inspiration  (187) 
and  also  the  student  who  has  the  least  difference  in  the  two 
figures,  to  try  the  experiment.  State  whether  or  not  there  is  a 
correspondence  between  chest  enlargement  and  lung  capacity. 

190.  How  air  is  forced  out  of  the  lungs.  —  As  soon  as  the 
muscles  that  cause  the  upward  movement  of  the  ribs  and  the 
downward  movement  of  the  diaphragm  begin  to  relax,  the 
ribs  sink  back  into  their  former  position,  the  breastbone 
is  pulled  back  into  place,  and  the  distended  wall  of  the  ab- 
domen presses  the  organs  upward  against  the  diaphragm, 
which   therefore   becomes   more    arched    (Fig.  42).     In   all 
these  ways  the  walls  of  the  chest  cavity  close  in  upon  the 
lungs,  and  thus  help  their  elastic  tissue  to  force  out  the  air 
in  expiration.     Ordinary   expiration    is    thus    accomplished 
without  muscular  effort. 

IV.   HYGIENE  OF  THE  RESPIRATORY  ORGANS 

191.  Hygienic    habits    of    breathing.  —  We    have    called 
attention    to    the    admirable    provisions    in    the    nose    for 
filtering  the  air.     Air  is  likewise  warmed  and  moistened  by 
the  mucous  membrane  of  the  nose.     This  is  necessary,  be- 
cause very  cold  or  very  dry  air  is  irritating  to  the  air  passages 


RESPIRATION  AND  ENERGY  IN  MAN 


133 


and  the  lungs.  Less  efficient  arrangements  for  this  purpose 
are  found  in  the  mouth  cavity.  Hence,  if  one  breathes 
through  the  mouth,  one  is  likely  to  take  in  considerable 
quantities  of  dust  and  bac- 
teria, which  may,  in  time, 
cause  inflammation  or 
other  forms  of  disease. 

192.  Effect   of   exercise 
on  respiration.  —  Not  only 
does  the  heart  beat  more 
rapidly  during  exercise,  but 
the  rate  of  breathing  also 
increases.     Oxygen  is  thus 
supplied    to    the    cells    in 
larger  quantities,  and  more 
wastes  are  eliminated. 
Deep  breathing  is  a  prime 
requisite  for  healthful  liv- 
ing, since  in  this  way  the 
air  is  changed  throughout 
the  lungs.     In  short,  quick 
breathing,    on    the    other 
hand,  it  is  only  the  air  in 

the  upper  regions  of  the  lungs  that  is  thus  affected.  The 
"  second  wind  "  that  the  runner  gets  after  a  short  time  is 
due  to  the  expansion  of  all  portions  of  the  lung  tissue.  In 
order  to  keep  the  chest  walls  flexible  and  capable  of  full  en- 
largement, a  certain  amount  of  regular  exercise  should  be 
persisted  in  throughout  life. 

193.  Effect   of    tight   clothing   upon  respiration.  —  In  an 
earlier  part  of  this  chapter  we  learned  that  air  is  forced  into 
the  lungs  when  the  front  ends  of  the  ribs  are  elevated  and  the 


A  =  inspiration. 


B  =  expiration. 


FIG.  42. —  Diagram  to  show  changes  in 
the  size  of  the  chest  cavity  during  in- 
spiration and  expiration. 

Ab  =  abdominal  wall. 
D  =  diaphragm. 
St  —  breastbone. 
Tr  =  windpipe. 


134  HUMAN  BIOLOGY 

diaphragm  is  pulled  downward  toward  the  horizontal  posi- 
tion. By  no  other  means'  are  the  respiratory  organs  filled 
with  air,  and  any  interference  with  the  action  of  either  ribs 
or  diaphragm  tends  to  decrease  the  supply  of  oxygen  and 
the  excretion  of  carbon  dioxid,  and  to  increase  the  chances 
of  disease  in  these  organs.  Tight  clothing  about  the  chest 
and  abdomen  not  only  results  in  permanent  distortion  of 
the  skeleton  (Fig.  46),  but  also  it  retards  the  movements  by 
which  the  chest  cavity  is  enlarged.  Shortness  of  breath  and 
inability  to  perform  any  great  amount  of  muscular  exercise 
are  some  of  the  ill  effects  that  are  experienced  from  tight 
lacing.  Diseased  conditions  of  the  organs,  too,  may  be 
brought  about  when  they  are  thus  compressed  and  forced 
out  of  position.  It  is  especially  important  that  loose  cloth- 
ing be  worn  in  the  gymnasium,  or  during  any  vigorous 
exercise,  in  order  that  the  muscles  used  in  motion  and  respir- 
ation may  be  free  to  work  unhampered. 

194.  Diseases  of  the  respiratory  organs.  —  In  26-34  we 
discussed  the  cause,  treatment,  and  prevention  of  pneu- 
monia, diphtheria,  and  tuberculosis,  all  of  which  affect  the 
organs  of  respiration.  We  shall  now  call  attention  to  some 
other  diseased  conditions  often  found  in  these  parts  of  our 
bodies.  Catarrh  is  an  inflammation  of  the  mucous  mem- 
branes of  the  throat  and  nose,  and  it  sometimes  becomes  so 
bad  that  these  air  passages  are  more  or  less  closed,  and  it 
causes  a  very  disagreeable  breath. 

.  Within  the  nose  and  throat  cavities  projections  from  the 
walls  frequently  develop,  which  at  times  practically  close 
these  air  passages  and  compel  the  individual  to  breathe 
through  the  mouth.  These  are  known  as  adenoids.  Be- 
tween the  mouth  and  throat  cavities  lie  the  tonsils;  if  these 
become  unduly  enlarged,  and  inflammation  sets  in,  tonsillitis 


EESPIRATION  AND  ENERGY  IN  MAN  135 

results.  As  soon  as  catarrh  or  enlarged  tonsils  or  adenoids 
are  discovered,  the  advice  of  a  competent  physician  should 
be  sought,  for  these  diseases  of  the  air  passages  prevent  an 
adequate  supply  of  air  from  reaching  the  lungs  and  tissues, 
and  seriously  interfere  with  the  normal  development  of  the 
body  and  mind. 

Colds  are  inflammations  of  the  air  passages  or  of  other 
regions  of  the  body,  and  they  are  probably  due  to  the  action 
of  bacteria.  If  the  malady  is  confined  to  the  nose  cavity,  we 
call  it  a  cold  in  the  head ;  if  it  is  seated  in  the  throat,  a  sore 
throat  results ;  a  cold  on  the  chest  is  an  inflammation  of  the 
windpipe  or  its  subdivisions.  When  the  bronchial  tubes 
are  affected,  their  lining  membrane  becomes  swollen,  and 
the  air  passages  are  more  or  less  closed;  this  is  bronchitis. 
And  finally,  if  the  inflammation  affects  the  air  sacs,  pneu- 
monia results. 

195.  Suffocation.  —  We  have  often  called  attention  to  the 
fact  that  the  body  must  be  supplied  continually  with  oxygen 
and  that  its  wastes  must  be  constantly  removed.  If  this 
process  is  interrupted,  even  for  five  minutes,  fatal  results 
are  almost  sure  to  follow.  If,  in  swallowing,  food  gets  past 
the  epiglottis  into  the  windpipe,  choking  results.  In  cases 
of  this  kind  the  head  should  be  held  forward  (or  downward 
in  case  of  a  child)  and  sharp  blows  struck  between  the 
shoulders.  By  suf-fo-ca'tion  is  meant  some  interference  with 
the  process  of  breathing.  Suffocation  may  be  due  to  in- 
closure  in  a  small  space  with  a  limited  supply  of  oxygen,  to 
the  inhaling  of  poisonous  gases,  or  to  immersion  in  water 
(drowning).  In  any  case,  the  patient  should  be  brought 
out  at  once  into  fresh  air.  If  water  has  entered  the  air 
passages,  the  person  should  be  turned  face  downward.  One 
should  then  stand  astride  him  and  support  the  weight  of  his 


136  HUMAN  BIOLOGY 

body  by  clasping  the  hands  beneath  his  abdomen.  In 
this  position  the  water  can  flow  out  of  his  lungs  more 
easily.  If  respiration  is  feeble,  cold  water  should  be  ap- 
plied to  his  face,  and  his  chest  should  be  slapped  vigor- 
ously. If  all  these  methods  fail  to  restore  vitality,  'and  if  the 
aid  of  a  physician  cannot  be  immediately  secured,  artificial 
respiration  should  be  attempted  at  once.1  This  is  accom- 
plished by  laying  the  patient  on  his  back,  with  a  rolled  coat 
or  other  support  beneath  his  shoulders.  His  mouth  should 
be  opened  and  his  tongue  drawn  out.  His  arms  should  then 
be  grasped  firmly  at  the  elbows  and  pulled  upward  and 
parallel  to  each  other  until  they  lie  above  the  head.  In 
this  way  air  is  drawn  in  through  the  nose  and  mouth. 
When  the  elbows  are  carried  downward  and  pressed  upon  the 
chest,  the  air  is  forced  out  of  the  body.  These  two  move- 
ments should  be  alternated  regularly  every  few  seconds,  and 
hope  of  resuscitation  should  not  be  abandoned  until  several 
hours  have  elapsed. 

196.  Necessity  of  ventilation.  —  Every  act  of  respira- 
tion removes  oxygen  from  the  air  taken  into  the  body,  and 
adds  to  the  air  carbon  dioxid  and  certain  poisonous  organic 
compounds.  One  might  breathe  in  this  air  a  second  time 
and  still  be  able  to  extract  oxygen  from  it.  The  presence 
of  chemically  pure  carbon  dioxid  in  air  even  in  considerable 
quantity  is  not  necessarily  dangerous ;  but  to  take  into  the 
body  again  the  organic  wastes  that  have  once  been  given  off 
is  most  unhealthful.  The  first  effect  of  foul  air  is  a  feeling 
of  sleepiness,  followed  by  headache,  and  if  larger  quantities 
are  breathed  in,  the  body  becomes  poisoned.  We  see,  then, 
the  absolute  necessity  of  having  the  air  in  a  living  room 

1  Pupils  should  learn  by  actual  practice  on  one  another  at  home 
the  movements  necessary  for  causing  artificial  respiration. 


RESPIRATION  AND  ENERGY  IN  MAN  137 

changed  frequently.  The  air  that  has  been  once  used  must  be 
removed  and  a  fresh  supply  must  be  furnished;  this  is  what  is 
meant  by  ven-ti-laftion. 

197.  Methods  of  ventilation.  —  It  is  important  to  re- 
member that  fresh  air  is  not  necessarily  cold  ah-,  and  that 
draughts  of  air  in  a  room  are  not  required ;  indeed,  that  they 
are  undesirable.  The  problem  of  ventilation  is  that  of  fur- 
nishing a  sufficient  quantity  of  wholesome  air  of  the  proper 
temperature  and  moisture  and  of  removing  the  foul  air.  It 
is  evident  that  this  is  rather  difficult  to  accomplish  in  school- 
rooms or  in  public  halls.  Air  will  not  of  itself  circulate 
rapidly  enough,  and  so  it  has  to  be  forced  into  these  rooms 
by  large  blowers  or  revolving  fans  in  the  basement.  This 
air  should  be  filtered  and  moistened.  Hot-air  pipes  or  fans 
are  likewise  often  employed  at  the  top  of  the  ventilating 
flues  to  draw  out  the  foul  air.  Since  warm  air  is  lighter  than 
cool  air,  the  former  should  enter  a  room  near  the  ceiling.  As 
it  cools  it  gradually  settles  toward  the  floor,  and  the  openings 
into  the  ventilating  shafts  should  be  found  at  the  lower  part 
of  the  room.  If  the  system  works  properly,  there  will  be 
a  continuous  supply  of  clean,  warm,  moist  air,  and  at  the 
same  time  the  air  that  has  once  been  used  will  be  drawn  off 
through  the  flues. 

Unfortunately,  in  most  of  our  dwelling  houses,  little  pro- 
vision has  been  made  by  the  builders  for  proper  ventilation. 
Hence,  if  the  rooms  are  heated  by  steam,  we  frequently 
breathe  the  same  air  over  and  over.  This  may  be  obviated, 
however,  by  ventilating  in  the  following  way.  A  piece  of 
board  two  or  three  inches  wide  should  be  fitted  across  the 
lower  end  of  the  window  opening.  When  the  lower  sash 
is  pulled  down  upon  it,  a  space  is  left  between  the  upper  and 
lower  sashes,  through  which  fresh  air  may  enter  the  room 


138  HUMAN  BIOLOGY 

without  causing  a  direct  draught.  In  order  to  secure  a 
proper  circulation  of  air  an  opening  of  equal  size  should  be 
provided  by  lowering  the  top  sash  of  the  window. 

Furnace  heat  is  much  more  satisfactory  than  steam  from 
the  point  of  view  of  ventilation,  for  in  this  way  a  continual 
supply  of  fresh,  warm  air  may  be  furnished.  An  open  fire- 
place is  one  of  the  best  means  of  removing  foul  air,  and  when 
a  fire  is  burning,  a  strong  current  up  chimney  is  assured.  We 
have  called  attention  to  the  fact  that  dry  heat  tends  to  cause 
catarrh  and  other  diseases  of  the  air  passages.  Provision 
should  therefore  be  made  to  keep  the  air  in  rooms  moist. 
This  may  be  partially  accomplished  by  keeping  the  water 
pans  in  a  furnace  full  of  water,  or  by  leaving  trays  of  water 
on  steam  or  hot  water  radiators. 


CHAPTER   VIII 

ADDITIONAL   TOPICS    IN   HUMAN   BIOLOGY 
I.   THE  SKIN 

198.  Characteristics  of  the  skin.  —  The  whole  outer  surface  of 
our  bodies  is  incased  in  a  flexible,  elastic  skin  of  varying  thickness 
and  texture.     In  regions  like  the  palm  of  the  hand  and  the  sole  of 
the  foot,  for  instance,  the  skin  is  thick  and  tough ;  the  covering  of 
the  lips,  on  the  other  hand,  is  extremely  thin.     At  the  ends  of  the 
fingers  and  toes  are  the  nails.    All  other  parts  of  the  body,  with 
the  exception  of  the  palms  of  the  hands  and  the  soles  of  the  feet, 
have  a  covering  of  hair.     Both  the  hair  and  the  nails  are  modified 
parts  of  the  skin. 

199.  Uses  of  the  skin.  —  The  most  obvious  use  of  the  skin  is 
the  protection  that  it  affords  to  the  muscles  and  other  organs  that 
lie  beneath.     In  the  second  place,  it  has  a  countless  number  of  sense 
organs  which  receive  messages  from  the  outside  of  the  body.    These 
are  carried  along  nerve  fibers  to  the  spinal  cord  and  brain,  and  then 
we  get  impressions  of  temperature,  of  pressure,  and  of  pain.     In  the 
third  place,  by  means  of  the  perspiratory  action  of  the  skin,  the  body 
throws  off  a  great  deal  of  water  and  small  quantities  of  other  waste 
matters.     And,  finally,  as  a  result  of  the  evaporation  of  this  water 
from  its  outer  surface,  the  body  loses  its  surplus  of  heat,  and  so 
keeps  an  even  temperature  of  98.6°  F. 

As  we  might  infer  from  all  these  uses,  the  skin  is  a  complex  organ 
composed  of  several  tissues.  We  shall  now  study  its  structure  and 
see  how  it  is  adapted  •  to  perform  the  four  functions  that  we  have 
just  enumerated. 

200.  Layers  of  the  skin.  —  The  skin  everywhere  consists  of  two 
different  layers  :  an  outer,  called  the  ep-i-der'mis  (Greek  epi  =  upon 

139 


140 


HUMAN  BIOLOGY 


+  derma  =  skin),  and  an  inner,  the  der'mis  (Fig.  43).  When  one 
gets  a  blister  by  burning  the  skin,  most  of  the  epidermis  is  lifted  up 
by  an  excessive  amount  of  watery  fluid  that  comes  from  the  blood. 
In  a  blister  one  can  easily  distinguish  the  white  epidermis  from  the 
pink  layers  of  the  dermis  lying  beneath. 

201.    Glands  of  the  skin.  —  Two  kinds  of  glands  are  found  in  the 
skin ;  namely,  the  oil  glands  and  the  sweat  or  per-spi'ra-to-ry 


duct  of 
sweat  gland 
hair 


2pidermis 


dermis 


hair  follicle 


sweat  gland 


atty  tissue 


papilla  of  hair 
FIG.  43.  — Vertical  section  of  scalp,  highly  magnified. 


The  former  are  found  in  most  parts  of  the  skin,  being  most  numer- 
ous in  the  scalp  and  in  the  skin  of  the  face.  Like  hairs,  however, 
oil  glands  are  wanting  on  the  palms  of  the  hands  and  the  soles  of  the 
feet.  Sweat  glands,  on  the  other  hand,  are  most  numerous  in  the 
regions  just  named.  One  writer  estimates  that  there  are  2800  sweat 


ADDITIONAL    TOPICS  IN  HUMAN  BIOLOGY        141 

pores  on  every  square  inch  of  the  surface  of  the  palm,  and  that  the 
total  number  of  these  glands  in  one's  skin  is  about  2,500,000. 

202.  Importance  of  bathing.  —  The  oil  glands   and  perspiratory 
glands  are  constantly  pouring  their  secretions  in  greater  or  less  quan- 
tity upon  the  skin.    As  the  water  evaporates,  the  oil  and  the  solid 
ingredients  of  the  sweat  are  left  behind.     Unless  these  are  removed, 
they  tend  to  clog  the  openings  of  the  ducts  from  the  glands  and  so  to 
interfere  with  the  work  of  the  skin.     A  considerable  amount  of  these 
substances  is  doubtless  worn  away,  together  with  the  scales  of  the 
outer  skin,  by  friction  against  the  clothing.     But  if  the  skin  is  to 
carry  on  its  functions  to  the  best  advantage,  and  if  decency  is  to  be 
maintained,  frequent  baths  must  be  taken. 

203.  Kinds  of  baths.  —  The  oily  secretions  and   much  of  the 
accumulated  dirt  on  exposed  surfaces  of  the  skin  can  be  removed  only 
by  the  use  of  warm  water  and  soap ;  hence  these  should  be  employed 
upon  the  hands  two  or  three  tunes  a  day  and  at  least  once  or  twice  a 
week  upon  the  whole  body.     Warm  baths  should  be  employed,  how- 
ever, for  their  cleansing  effect  only,  since  they  are  usually  followed 
by  a  feeling  of  lassitude.     One  is  much  more  likely  to  catch  cold,  too, 
after  exposure  to  warm  water,  as  it  opens  the  pores  of  the  skin,  causes 
the  arteries  near  the  surface  to  dilate,  and  thus  increases  the  amount 
of  perspiration.     Unless  the  warm  bath  is  taken  just  before  going 
to  bed,  it  should  be  followed  by  a  quick  application  of  cold  water. 

Cold  baths,  on  the  other  hand,  if  taken  under  proper  conditions, 
have  an  exhilarating  effect.  The  body  should  then  be  rubbed  vigor- 
ously with  a  coarse  towel.  If  after  a  cold  bath  one  does  not  feel  a 
warm  glow,  the  bath  is  injurious  rather  than  beneficial. 

Baths  should  never  be  taken  immediately  after  eating,  since  the 
blood  is  thereby  drawn  away  from  the  organs  of  digestion.  Nor 
should  one  remain  in  cold  water  until  one  feels  a  chill.  Shower 
baths,  however,  are  better  than  a  cold  plunge,  for  they  stimulate 
both  by  the  cool  temperature  of  the  water  and  by  the  force  with 
which  it  strikes  the  skin. 

204.  Care  of  the  hair.  —  The  oil  glands   are  most  numerous  in 
the  scalp,  and  if  the  skin  is  in  a  healthy  condition,  the  hair  is  supplied 


142  HUMAN  BIOLOGY 

« 

with  the  proper  amount  of  oil.  If  this  secretion  dries,  however, 
and  becomes  mixed  with  the  loose  outer  scales  of  the  epidermis, 
dandruff  is  caused,  and  this  should  be  removed  by  vigorous  brushing 
and  shampooing.  Not  only  is  the  scalp  cleaned  in  both  of  these  ways 
(if  clean  brushes  and  combs  are  used),  but  the  friction  stimulates 
the  circulation  of  the  blood  through  the  scalp,  and  good  blood  is  a 
better  hair  tonic  than  any  external  application.  If  the  oil  supply  is 
insufficient  and  the  hair  becomes  dry,  vaseline  may  be  used.  The 
scalp  should  be  well  dried  after  a  bath,  for  moisture  at  the  roots  of 
the  hair  tends  to  cause  decomposition.  Brushes  and  combs  should 
be  kept  scrupulously  clean. 

205.  Care  of  the  nails.  —  One  of  the  surest  means  of  detecting 
slovenly  personal  habits  is  by  watching  the  care  an  individual  takes 
of  his  finger  nails.     An  accumulation  of  dirt  beneath  the  nails  or 
jagged  edges  caused  by  biting  the  nails  almost  always  indicate  a  lack 
of  good  breeding.     The  finger  nails  should  be  carefully  cleaned  with 
soap,  water,  and  a  nail  brush  or  with  a  nail  cleaner,  but  never  with  a 
penknife  or  scissors,  for  metal  scratches  the  surface  and  makes  a 
place  for  the  lodgment  of  dirt.     The  roll  of  epidermis  about  the  base 
of  the  nail  should  frequently  be  moistened  and  pushed  back ;   other- 
wise this  outer  skin  is  likely  to  become  torn  and  to  form  the  so-called 
"  hangnails."    These  are  often  a  source  of  great  discomfort  and 
sometimes  of  danger,  for  they  furnish  a  possible  opening  for  infec- 
tion by  bacteria. 

206.  Treatment   of  burns.  —  We  have    already  suggested  the 
treatment  for  cuts  and  bruises  of  the  skin  in  26.     Another  form  of 
accident  that  may  injure  the  skin  is  a  burn.     The  affected  part 
should  be  covered  and  bandaged  with  a  paste  of  baking  soda,  which 
tends  to  lessen  the  pain  by  keeping  out  the  air.     A  mixture  (known 
as  carron  oil),  half  linseed  oil  and  half  limewater,  is  also  a  good 
remedy  to  keep  on  hand  for  burns.     If,  however,  the  skin  is  broken, 
the  wound  should  be  treated  with  an  antiseptic.     When  the  cloth- 
ing of  a  person  catches  fire,  the  flames  should  be  extinguished  by 
wrapping  him  quickly  in  thick  clothing  or  pieces  of  carpet. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY       143 

207.  Clothing.  —  The  warmth  of  certain  kinds  of  cloth  depends 
upon  the  fact  that  they  keep  the  heat  of  the  body  from  escaping ; 
in  other  words,  they  are  poor  conductors  of  heat.     Good  conductors, 
on  the  other  hand,  allow  the  heat  to  pass  off  rapidly.    This  differ- 
ence in  fabrics  is  largely  due  to  the  way  they  are  woven.    Wool,  for 
instance,  is  usually  made  into  cloth  that  is  loose  in  texture,  and  thus 
it  can  hold  a  considerable  amount  of  air  in  its  meshes.     Now,  dry  air 
is  a  poor  conductor  of  heat.     Woolen  clothing  is,  therefore,  generally 
used  for  winter  wear.     Cotton  and  linen  are  tightly  woven,  and  heat 
radiation  through  these  materials  is  rapid.     When  this  takes  place, 
the  blood  is  likely  to  be  driven  away  from  the  surface  of  the  body, 
thus  causing  a  congestion  of  blood  in  the  internal  organs,  which  is  a 
favorable  condition  for  such  diseases  as  colds,  pneumonia,  or  con- 
sumption.    The  same  result  often  follows  the  wearing  of  wet  cloth- 
ing, since  wet  clothing  is  a  good  conductor  of  heat. 

208.  Effect  of  alcohol  on  body  temperature.  —  "  The  action  of 
alcohol  in  loivering  the  temperature,  even  in  moderate  doses,  is  most 
important.     By  dilating  the  cutaneous  vessels,  it  thus  permits  of  the 
radiating  of  much  heat  from  the  blood.     When  the  action  is  pushed 
too  far,  and  especially  when  this  is  combined  with  the  action  of  great 
cold,  its  use  is  to  be  condemned." l 

"  A  party  of  engineers  were  surveying  in  the  Sierra  Nevadas. 
They  camped  at  a  great  height  above  the  sea  level,  where  the  air  was 
very  cold,  and  they  were  chilled  and  uncomfortable.  Some  of 
them  drank  a  little  whisky,  and  felt  less  uncomfortable ;  some  of 
them  drank  a  lot  of  whisky,  and  went  to  bed  feeling  very  jolly  and 
comfortable  indeed.  But  in  the  morning  the  men  who  had  not  taken 
any  whisky  got  up  in  a  good  condition ;  those  who  had  taken  a  little 
whisky  got  up  feeling  very  miserable ;  the  men  who  had  taken  a  lot 
of  whisky  did  not  get  up  at  all :  they  were  simply  frozen  to  death. 
They  had  warmed  the  surface  of  their  bodies  at  the  expense  of  their 
internal  organs."  2 

1  Landois  and  Stirling,  "Textbook  of  Human  Physiology." 

2  T.  Lauder  Brunton,  London,  "Lectures  on  the  Action  of  Medi- 
cine." 


144  HUMAN  BIOLOGY 

II.   THE  SKELETON 

209.  Necessity  for  the   skeleton.  —  Most  of  the  common  ani- 
mals with  which  we  are  familiar  have  some  kind  of  skeleton  that 
serves  as  a  means  of  protection,  of  support,  or  of  locomotion.     In 
some  animals,  e.g.  clams  and  lobsters,  the  skeleton  is  on  the  outside  ; 
in  the  vertebrates,  on  the  other  hand,  the  skeleton  is  internal.     A 
study  of  Figure  44  will  make  clear  the  general  arrangement  of  the 
skeleton  of  man.     The  position  and  general  shape  of  the  bones  may 
be  determined  by  the  pupil  from  a  study  of  his  own  body.     For  con- 
venience, the  two  hundred  bones  of  the  skeleton  may  be  divided  into 
three  groups,  namely,  (1)  the  bones  of  the  neck  and  trunk,  (2)  the 
bones  of  the  arms  and  legs,  and  (3)  the  bones  of  the  head. 

210.  The  skeleton  of  the  neck  and  trunk.  —  The  erect  position  of 
the  adult  human  body  is  maintained  by  a  column  of  bones  called 
vertebrce.     The  spinal  column  may  be  felt  through  the  skin  behind  the 
neck  and  down  the  middle  of  the  back.     The  human  spinal  column 
is  a  wonderful  piece  of  mechanism,  which  by  its  structure  is  adapted 
to  perform  at  the  same  time  three  distinct  functions.     In  the  first 
place,  the  vertebrae,  piled  one  on  the  other,  form  a  column  strong 
enough  to  support  the  weight  of  the  body.     Again,  the  structure  of 
the  spinal  column  shows  marvelous  provisions  for  securing  elasticity 
and  freedom  of  motion.    Elasticity  is  secured  by  a  succession  of  four 
curves  which  are  best  seen  in  a  side  view  of  the  body.     By  means  of 
these  curves  the  head  and  the  upper  part  of  the  trunk  are  saved  from 
sudden  shocks  that  would  result  from  running  or  jumping,  for  the 
curves  act  like  a  series  of  springs.     Pads  of  cartilage  between  the 
vertebrae  serve  as  cushions  to  prevent  jarring.      This  general  ar- 
rangement of  the  spinal  column  permits  a  considerable  range  of 
movement. 

A  third  adaptation  that  is  evident  in  the  structure  of  the  spinal 
column  is  the  protection  it  affords  to  the  delicate  spinal  cord  (231) 
which  is  inclosed  by  it  in  a  continuous  tube.  One  would  search 
far  before  finding  a  more  perfect  means  of  securing  strength,  elas- 
ticity, and  flexibility  than  that  provided  in  the  structure  of  the 
human  spinal  column. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY       145 


upper  jaw  bone 
lower  jaw  bone 

collar  bone 


upper  arm  bone 
(humerus) 


ribs 


bones   f  (radius) 

of      \ 
forearm  [  (ulna) 


kneecap 


fibula 


vertebrae 


shoulder  blade 
breast  bone 


shin  bone  (tibia) 


FIG.  44. — Skeleton  of  man. 


146  HUMAN  BIOLOGY 

Attached  to  the  spinal  column  are  twelve  pairs  of  ribs,  ten  pairs 
of  which  connect  with  the  breastbone  and  thus  help  to  inclose  the 
chest  cavity  (Fig.  44).  The  arms  are  attached  to  the  rest  of  the 
skeleton  by  a  movable  girdle  of  bones  consisting  of  the  two  shoulder 
blades  and  the  two  collar  bones.  A  complete  and  rigid  circle  of  bones 
is  formed  at  the  posterior  end  of  the  trunk  by  the  two  pelvic  bones, 
which  are  attached  dorsally  to  the  spinal  column  and  meet  in  front. 
On  the  outer  side  of  each  pelvic  bone  is  a  deep  socket  into  which  fits 
the  upper  end  of  the  thigh  bone  (Fig.  44) . 

211.  Skeleton  of  the  arm.  —  The  skeleton  of  the  upper  arm  (see 
Fig.  44)  is  formed  by  a  single  long  bone  called  the  hu'me-rus,  which 
extends  from  the  shoulder  to  the  elbow.     In  the  forearm,  one  can 
feel  through  the  flesh  two  separate  long  bones,  of  about  the  same 
size,  lying  side  by  side ;  the  bone  on  the  thumb  side  of  the  forearm 
is  the  ra'di-us;   on  the  little  finger  side  is  the  ul'na.     Eight  small 
bones  are  found  in  the  wrist ;   and  in  the  palm  of  the  hand  and  in 
the  fingers  are  nineteen  somewhat  elongated  bones.     All  these 
twenty-seven  bones  move  freely  upon  each  other  and  thus  give  the 
hand  a  great  freedom  of  movement. 

212.  Skeleton  of  the  leg.  —  In  the  upper  part  of  the  leg  (see  Fig. 
44)  is  a  single  bone,  the  thigh  bone  or  fe'mur.    This  corresponds  in  po- 
sition to  the  humerus  of  the  arm,  but  it  is  longer  and  stouter  than 
the  latter ;  in  fact,  it  is  the  longest  bone  in  the  body.     The  skeleton 
in  the  calf  of  the  leg  consists  of  two  bones  (tib'i-a  and  fib'u-la) 
which  have  a  position  similar  to  that  of  the  radius  and  ulna.     The 
tibia  is  on  the  inner  or  great-toe  side  and  is  much  larger  than  the 
slender  fibula.     At  the  knee  joint  one  can  feel  a  flat  piece  of  bone, 
more  or  less  circular  in  outline,  called  the  kneecap.    The  twenty-six 
bones  of  the  ankle  and  foot  are  in  the  form  of  an  arch,  one  end  of 
which  rests  upon  the  heel. 

213.  Skeleton  of  the  head.  —  Two  groups  of  bones  may  be  dis- 
tinguished in  the  skull  or  skeleton  of  the  head ;  namely,  the  bones 
forming  the  cranium,  which  surrounds  and  protects  the  brain,  and 
the  bones  that  form  the  skeleton  of  the  face  (Fig.  44). 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY       147 


By  its  rounded  contour,  the  skull  furnishes  the  best  possible  pro- 
tection for  the  brain.  In  the  first  place,  if  a  blow  strikes  upon 
the  head,  it  would  be  much  more  likely  to  glance  off  than  would  be 
the  case  if  the  sides  and  top  were  flat. 

Since  the  end  of  the  nose  and  the  outside  ear  are  the  most  exposed 
portions  of  the  head,  they  would,  if  made  of  bone,  be  in  constant 
danger  of  getting  broken.  Cartilage,  however,  gives  them  suffi- 
cient permanence  of  form,  and  at  the  same  time  this  elastic  material, 
if  bent  out  of  shape,  at  once  returns 
to  its  original  position  as  soon  as 
the  pressure  is  removed. 

The  deep  eye  sockets  seldom 
allow  any  blow  to  injure  the  eye. 
The  drum  of  the  ear,  the  three  tiny 
bones  of  the  middle  ear,  and  the 
delicate  mechanism  of  the  inner  ear 
are  all  buried  deep  in  the  hardest 
part  of  the  skull,  and  so  these  are 
out  of  danger. 


ligament/- 
cartilage 


fibula 


bia 


FIG.  45.  —  Knee  joint. 


214.  Joints.  —  Thus  far  we  have 
considered  the  bones  of  the  skele- 
ton as  though  they  were  independent  of  each  other.  In  the  living 
body,  however,  we  know  that  they  are  firmly  attached  to  one  an- 
other by  ligaments  and  muscles,  and  that  thus  a  strong  but  mov- 
able framework  is  formed  (Fig.  45).  Any  region  in  the  skeleton 
where  motion  is  possible  between  two  bones  is  called  a  joint. 

216.  Food  and  the  skeleton.  —  In  the  composition  of  bones, 
mineral  is  found  to  constitute  about  two  thirds  of  the  material, 
and  this  must  be  supplied  by  the  food. 

Milk  is  a  most  important  article  of  diet  in  early  Me,  since  in  addi- 
tion to  the  other  nutrients,  it  supplies  the  phosphate  of  lime  needed 
for  bone  manufacture.  In  the  process  of  refining  wheat  flour  much 
of  the  mineral  matter  is  lost ;  for  this  reason  whole  wheat  flour  and 
the  coarser  cereals  like  corn,  rye,  and  oats  are  much  more  valuable 
as  bone  builders,  and  are  especially  needful  during  the  period  of 


148 


HUMAN  BIOLOGY 


growth.  The  mineral  matters  in  our  foods  are  made  soluble  and 
are  then  supplied  by  the  blood  to  the  bone  cells,  and  these  in  turn 
convert  this  mineral  matter  into  the  hard  intercellular  substance. 

216.  Effect  of  pressure  on  bones.  —  Tight-fitting  clothing  is  a 
most  important  factor  in  modifying  permanently  the  shape  and  po- 
sition of  bones.  Normal  growth  cannot  be  attained  if  the  skeleton 
is  subjected  to  pressure.  Yet  this  important  principle  of  hygiene  is 
constantly  violated  by  women  who  wear  tight-fitting  clothing  about 


A  =  Normal  position  of  organs.      B  =  Position  of  organs  after  lacing. 
FIG.  46.  —  Effect  of  tight  lacing  on  the  organs  of  the  chest  and  abdomen. 

the  waist.  Baneful  fashion  is  often  followed  even  in  youth,  when  the 
skeleton  yields  readily  to  pressure.  The  result  is  that  the  ribs  are 
permanently  bent  downward  and  inward,  thus  interfering  seriously 
with  the  action  of  the  abdominal  organs  (Fig.  46).  High-heeled 
shoes  are  another  frequent  cause  of  deformity.  They  reduce  the 
spring  in  the  arch  of  the  foot  and  throw  too  much  of  the  weight  of 
the  body  upon  the  tips  of  the  toes,  and  this  is  likely  to  injure  the 
arch  of  the  foot.  Shoes  with  narrow  toes  should  never  be  worn, 
since  by  this  means  the  foot  is  deformed. 

217.    Fractures.  —  Any  sudden  strain  or  blow  upon  a  bone  is 
liable  to  cause  a  break  or  a  fracture,  especially  in  later  life,  when  the 


ADDITIONAL    TOPICS  IN  HUMAN  BIOLOGY        149 

bones  are  brittle.  Fractures  occur  more  commonly  in  the  shafts  of 
long  bones,  and  they  may  usually  be  recognized  by  the  fact  that  an 
extra  joint  is  thus  formed  and  by  the  fact  that  the  broken  ends  grate 
against  each  other. 

In  treating  a  fracture,  the  pieces  of  bone  must  be  brought  back 
into  position  (this  is  called  "  setting  "  the  bone),  and  must  be  held 
in  place  by  splints  until  the  ends  have  become  firmly  "  knit "  to- 
gether. The  setting  of  a  bone  should  only  be  attempted  by  a  sur- 
geon. In  general  but  two  rules  should  be  followed  in  case  of  a  frac- 
ture :  first,  send  for  a  doctor;  second,  keep  the  broken  bone  perfectly 
quiet  in  as  comfortable  a  position  as  possible.  Hot  or  cold  water  ap- 
plications if  applied  at  once  often  reduce  the  pain  and  prevent  in- 
flammation. Movement  at  the  point  of  fracture  almost  always 
causes  inflammation,  which  makes  the  setting  difficult;  and  if 
moved  suddenly,  the  surrounding  tissues  may  be  injured  as  well. 

218.  Dislocations.  —  A  dislocation  is  an  accident  to  a  joint  in 
which  the  ends  of  the  bones  are  forced  apart.     One  can  usually 
recognize  a  dislocation  by  the  unwonted  protrusion  of  the  bones,  and 
by  the  pain  caused  when  any  motion  at  the  joint  is  attempted. 
Since  ligaments  of  connective  tissue  bind  the  bones  together  rather 
closely,  a  dislocation  often  results  in  a  wrenching  or  tearing  of  the 
connective  tissue  about  a  joint ;    swelling  and  discoloration  follow 
quickly;   and  it  is  therefore  necessary  to  put  the  bones  back  into 
place,  or,  in  other  words,  to  "  reduce  the  dislocation  "  as  soon  as 
possible.     If  surgical  aid  can  be  procured,  it  is  better  to  apply  cold 
water  to  the  joint  and  wait  for  the  doctor's  arrival,  since  by  unskillful 
treatment  further  injury  to  the  joint  may  result.     When  skilled 
treatment  is  impossible,  most  dislocations  may  be  reduced  by  stead- 
ily pulling  the  bones  apart  until  it  is  possible  for  the  ends  to  glide 
back  into  place. 

219.  Sprains.  —  When  a  sudden  strain  causes  neither  a  fracture 
nor  a  dislocation,  it  often  gives  rise  to  a  twisting  or  tearing  of  liga- 
ments and  other  connective  tissues  in  the  region  of  a  joint.     Such  an 
accident  is  called  a  sprain.     The  injured  region  is  usually  swollen 
and  painful.     Since  it  is  difficult  to  distinguish  a  sprain  from  other 


150 


HUMAN  BIOLOGY 


attachments  of 
tendons  to 
radius 


accidents  to  the  skeleton,  medical  assistance  should  be  summoned 
and  the  following  directions  carefully  followed:  (1)  the  sprained 
member  should  be  placed  at  once  in  cold  water  or  in  hot  water 
and  held  there  for  some  time ;  (2)  arnica  or  witch  hazel  may  be 
applied;  (3)  the  sprain  should  then  be  bound  in  a  tight  bandage 
(these  three  applications  tend  to  keep  down  the  swelling);  and 
(4)  (most  important  of  all)  the  joint  should  have  complete  rest  until 
all  swelling  and  soreness  have  disappeared.  It  is  probable  that  more 
permanent  injuries  result  from  careless  treatment  of  sprains  than 
from  all  other  accidents  to  the  skeleton. 

III.   THE  MUSCLES 

220.  Importance  of  muscle  tissue.  —  Muscle  tissue  constitutes 
41  per  cent,  or  almost  half,  of  the  weight  of  the  human  body.    In  this 

kind  of  tissue  is  found  one 
fourth  of  all  the  blood.  But 
the  importance  of  muscle 

attendonTto°f  ^ssue  *s  appreciated,  even 
shoulder  more  fully,  when  we  realize 
that  practically  every  kind 
of  movement  in  the  body  is 
due  to  the  action  of  the  mus- 
cles. Not  only  do  they  bring 
about  the  more  obvious  mo- 
tions of  the  arms  (Fig.  47) ,  the 
legs,  the  trunk,  and  the  head, 
but  also  the  contractions  of 
the  heart,  of  the  stomach,  and 
of  the  other  internal  organs.  Every  change  in  the  expression  of  the 
face,  and  every  variation  in  the  tone  of  the  voice,  is  likewise  a  result 
of  the  action  of  this  all-important  tissue.  Hence  we  are  not  sur- 
prised that  there  are  over  five  hundred  separate  muscles,  which  vary 
in  length  from  the  fraction  of  an  inch  (within  the  ear  cavity)  to 
over  a  foot  and  a  half  (down  the  front  of  the  thigh) . 

221.  Kinds  of  muscle.  —  All  of  these  muscles  are  in  one  way  or 
another  under  the  control  of  the  nervous  system.     Some  of  them  are 


elbow 
FIG.  47. — Action  of  biceps  muscle. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY        151 

directed  by  the  conscious  portions  of  our  brain.  Thus  we  can  close 
our  fingers  and  open  them  as  we  please ;  we  can  move  the  eyes,  the 
head,  and  the  legs  at  will.  We  call  all  the  muscles  that  are  con- 
trolled by  our  will  power,  vol'un-ta-ry  muscles  (Lathi,  voluntas  = 
will).  Most  of  the  muscles  of  the  throat,  those  of  the  gullet,  stom- 
ach, and  intestines,  on  the  other  hand,  act  without  any  voluntary 
direction  on  our  part,  and  they  are  therefore  called  in-vol'un-ta-ry. 

222.  Conditions  necessary  for  healthy  muscles.  —  If  one  is  to 
have  a  well-developed  and  healthy  muscular  system,  four  conditions 
must  be  fulfilled :    the  body  must  be  supplied  with  nutritious  food; 
there  must  be  a  generous  amount  of  fresh  air;  the  muscles  must  be 
exercised  vigorously;  and  this  exercise  must  be  followed  by  periods  of 
rest.    We  will  now  consider  in  turn  how  each  of  these  requirements 
may  be  met. 

223.  Food. — We  have  learned  that  75  per  cent  of  muscle  is  com- 
posed of  water,  and  that  protein  is  the  most  important  solid  ingredi- 
ent.    Mineral  matter  and  fats  are  also  present  in  small  quantities, 
even  in  the  leanest  of  muscle.     During  the  period  of  growth  all  these 
nutrients  should  be  supplied  for  muscle  building,  but  protein  is 
absolutely  essential.     Grape  sugar  is  also  found  to  be  an  important 
food  during  muscular  contraction.    The  diet  of  athletes  while  they 
are  training  for  contests  is  carefully  regulated :   rare  meats,  coarse 
breads,  eggs,  vegetables,  and  fruits  are  supplied  in  generous  quanti- 
ties ;  pastry  and  fats  are  reduced  to  a  minimum.    Tobacco  and  al- 
cohol in  any  form,  however,  are  absolutely  prohibited.     Such  a  diet  is 
undoubtedly  far  more  wholesome  to  develop  a  healthy  boy  or  girl, 
man  or  woman,  than  are  the  rich  gravies,  pastries,  and  condiments 
which  are  found  on  too  many  tables. 

224.  Fresh  air.  —  Healthy  muscle  is  absolutely  powerless,  how- 
ever, unless,  in  addition  to  food,  it  receives  a  supply  of  oxygen ; 
for  all  muscular  energy  is  produced  by  oxidation.     Impure  air,  be- 
sides being  deficient  in  oxygen,  contains  carbon  dioxid  and  other 
gases  that   are  exceedingly  harmful  to  the  tissues   (196).     Well- 
ventilated  sleeping  rooms  are  most  essential  for  healthy  living,  for 


152  HUMAN  BIOLOGY 

during  the  night  the  body  gets  rid  of  much  of  the  waste  carbon 
dioxid  that  is  formed  during  the  day. 

225.  Exercise.  —  It  seems  like  a  contradiction  to  say  that  the 
only  way  to  get  more  and  better  muscle  is  to  destroy  what  we  al- 
ready have.  Every  one  knows,  however,  that  if  the  muscles  of  the 
arm  or  the  leg  are  not  used  for  a  time,  they  become  weak  and  flabby, 
and  yet  every  time  a  muscle  is  made  to  contract,  some  of  its  substance 
is  oxidized.  New  muscle,  formed  by  the  process  of  assimilation, 
must  take  its  place. 

A  certain  amount  of  vigorous  exercise  each  day  is  essential  if 
one's  body  is  to  be  kept  in  the  best  physical  condition.  This 
amount,  of  course,  varies  with  the  individual,  and  it  should  never  be 
carried  to  an  excess,  resulting  in  exhaustion.  Fortunate  is  the  boy 
who  can  spend  the  early  years  of  his  life  in  the  country,  and  who 
has  been  taught  to  do  a  certain  amount  of  manual  work  each  day  out 
of  doors.  Regularity  in  exercise  is  as  important  as  regularity  in 
eating.  One  cannot  exercise  vigorously  one  day  and  expect  its  good 
effects  to  last  for  a  week.  We  should  not  call  upon  the  muscles  for 
violent  exertion  immediately  after  rising  and  before  breakfast,  nor 
should  we  exercise  until  at  least  a  half  hour  after  eating.  The 
physiological  reasons  for  these  directions  have  already  been  given 
in  our  study  of  the  circulatory  system  (170) . 

The  best  forms  of  exercise  are  those  that  call  into  play  the  great- 
est number  of  muscles.  For  this  reason  gymnasium  training  is 
better  than  many  kinds  of  outdoor  sports.  In  the  gymnasium,  too, 
special  forms  of  exercise  may  be  taken  to  develop  any  muscles  found 
to  be  weak.  On  the  other  hand,  lawn  tennis,  golf,  rowing,  and  foot- 
ball have  the  additional  advantage  of  being  played  in  the  open  air, 
and  games  of  this  sort  are  usually  more  exhilarating  than  are  set 
forms  of  exercise  with  apparatus.  That  the  full  effect  of  any  kind 
of  exercise  may  be  attained,  it  should  be  followed  by  a  moderately 
warm,  then  by  a  cold,  shower,  or  sponge  bath,  and  by  a  good  rubbing 
of  the  body  with  a  coarse  towel. 

Muscles  are  not  the  only  tissues  developed  by  exercise.  Every 
muscular  contraction  is  directed  by  some  kind  of  stimulus  from  the 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY        153 


nervous  system.  Before  the  muscles  of  the  arm  or  leg  contract,  a 
"  message  "  must  come  to  them  from  the  brain  or  spinal  cord ;  hence 
nerve  tissue  is  likewise  developed  by  exercise. 

226.    Rest.  —  If  physical  exertion  is  carried  beyond  a  certain 
point,  exhaustion  results,  and  the  muscles  cannot  be  made  to  con- 
tract until  after  a  period 
of  rest.     Since  all  muscu- 
lar  contraction   involves 
oxidation   of   tissue,    pe- 
riods of  rest  must  be  al- 
lowed for  the  muscles  to 
get  rid  of  their  wastes  and 
to  build  up  new  tissue  in 
place  of   the   old.     The 
feeling  of  weariness  after 
long-continued  exercise  is 
probably  due  to  the  pres- 
ence in  the  body  of  great 
quantites    of 
oxid,    water, 
wastes.     One 
rest  to  good 
by    changing 


A  =  Correct  posture.  B  =  Incorrect  posture. 

FIG.  48.  —  Standing  positions. 


carbon  di- 

and   other 

can   often 

advantage 
_  _  from  one 
form  of  activity  to  an- 
other, but  from  eight  to 
nine  hours  of  sound  sleep 
each  night  are  indispen- 
sable for  the  health  of  a  growing  youth.  The  necessity  for  sleep 
will  be  further  discussed  in  the  study  of  the  nervous  system. 

227.  Relation  of  muscles  to  proper  posture.  —  An  erect  posture 
and  graceful  carriage  not  only  add  to  pleasing  appearance,  but  are 
important  in  maintaining  the  health.  Round  shoulders  and  stoop- 
ing position  decrease  the  capacity  of  the  chest  and  interfere  seriously 
with  the  action  of  its  organs.  It  is  important  that  boys  and  girls 
acquire  a  good  posture  early  in  life,  and  that  they  realize  that  this 


154 


HUMAN  BIOLOGY 


A  =  Correct  posture. 


B  =  Incorrect  posture. 


is  largely  a  matter  of  muscular  train- 
ing. In  standing  (Fig.  48) ,  the  head 
and  body  should  be  erect,  the  heels 
brought  close  together,  and  the 
shoulders  brought  into  such  a  posi- 
tion that  the  back  is  approximately 
flat.  In  sitting  (Fig.  49) ,  care  should 
be  taken  not  to  bend  the  body  over 
the  desk,  and  a  proper  relation 
between  height  of  chair  and  desk 
should  be  secured. 

Permanent  curvature  of  the  spine 
frequently  results  from  carrying 
loads  of  books  or  other  heavy  ob- 
jects on  one  side  of  the  body  only; 
pupils  should  therefore  train  them- 
selves to  use  the  arms  alternately 
for  this  purpose. 

IV.   THE  NERVOUS  SYSTEM 


228.  The  body  as  a  collection  of 
organs.  —  In  the  preceding  chap- 
ters we  have  discussed  the  diges- 
tive, respiratory,  and  circulatory 
systems  and  have  seen  that  these 
organs  furnish  all  parts  of  the  body 
with  food  and  oxygen.  We  have 
studied  the  process  of  oxidation 
whereby  we  keep  warm  and  gain 
the  power  to  do  work.  And  finally 
we  are  familiar  with  the  fact  that 
the  bones  and  muscles  are  the 
organs  that  give  support  to  the 
body  and  provide  the  machinery 

for  all  our  motions.    Thus  we  see  that  the  body  is  composed  of 
many  organs,  each  with  its  special  function  or  functions. 


C  =  Desk  and  seat  too  low. 
FIG.  49.  —  Sitting  positions. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY        155 

229.  Cooperation  of  the  organs.  —  But  a  human  being  is  more 
than  a  mere  collection  of  working  organs,  for  all  the  various  organs 
work  together  for  the  common  good.     This  is  what  we  mean  by  coopera- 
tion   (Latin,    co  =  together  +  operari  =  to    work).     Suppose   we 
take  a  few  instances  from  everyday  experience  to  illustrate  this 
cooperation. 

When  food  is  taken  into  the  mouth,  the  salivary  glands  pour  out 
upon  it  an  abundant  supply  of  saliva.  Now,  the  food  never  comes 
in  contact  with  the  glands.  How  is  it,  then,  that  they  send  out  their 
secretion  at  just  the  right  time  and  in  the  proper  amount? 

If  a  blow  is  aimed  at  one's  face,  one's  hands  immediately  fly  up  to 
ward  off  the  threatened  injury.  If  the  attack  were  pressed  and  one 
were  really  compelled  to  defend  himself,  his  heart  would  beat  much 
more  rapidly,  he  would  breathe  faster,  and  the  flow  of  perspiration 
would  become  evident.  During  the  contest  certain  feelings,  also, 
would  doubtless  be  aroused. 

230.  Functions  of  the  nervous  system.  —  All  the  succession  of 
activities  just  described  would  be  utterly  impossible  if  some  means 
were  not  provided  for  making  the  organs  work  together  for  the  com- 
mon good.    The  arms  could  not  see  to  strike  at  the  antagonist; 
nor  could  the  heart,  lungs,  or  skin  respond  to  the  sudden  exertion  of 
the  rest  of  the  body.     It  is  the  nervous  system  that  controls  the 
action  of  each  of  the  organs  in  the  body  and  brings  about  a  coopera- 
tion between  them.    All  our  sensations,  too,  and  our  will  power  are 
doubtless  correlated  with  the  activities  of  the  nervous  system. 

231.  Parts  of  the  nervous  system.  — -  The  nervous  system  con- 
sists of  nerve  centers  and  nerve  fibers  (of  which  nerves  are  composed). 
The  principal  nerve  centers  are  the  brain  and  spinal  cord  (Fig.  50). 
These  delicate  organs  are  inclosed  and  wonderfully  protected  by  the 
bony  cranium  and  spinal  column. 

From  the  brain  and  spinal  cord  pass  off  numerous  bundles  of 
nerves.  As  they  approach  the  different  organs  of  the  body  they 
divide  into  branches,  and  thus  the  nerves  become  smaller  and 
smaller.  Finally,  the  microscope  is  needed  to  trace  the  individual 
nerve  fibers  to  their  endings  ID  muscle,  gland,  or  sense  organ.  By 


FIG.  50.  —  General  arrangement  of  nervous  system. 
156 


ADDITIONAL    TOPICS  IN  HUMAN  BIOLOGY        157 


means  of  these  countless  nerve  fibers  all  parts  of  the  body  are  put  in 
communication  with  the  nerve  centers  (see  Fig.  50). 

232.  Cellular  structure  of  the  nervous  system.  —  If  a  section  is 
made  of  any  part  of  the  brain  or  spinal  cord,  two  kinds  of  material, 
known  respectively  as  gray  matter  and  white  matter,  may  be  distin- 
guished. In  the  gray  matter  are  countless  nerve  cells  (Fig.  51) 
which  are  very  irregular  in  form.  From  most  of  the  nerve  cells 
project  numerous  fine  processes  that  look  like  tiny  branching  roots. 
These  bring  the  various  nerve 
cells  into  communication  with 
each  other. 

One  fiber-like  process,  how- 
ever, has  fewer  branches  than 
the  others,  and  may  be  traced 
for  a  considerable  distance 
from  the  cell  body.  This  is 
the  beginning  of  a  nerve  fiber, 
and  it  is  the  mass  of  nerve 
fibers  that  make  up  most  of 
the  white  matter  of  the  nerv- 
ous system. 


FIG.  51.  —  Nerve  cell  from  spinal  cord. 


233.  Nerve  impulses.  —  We 
may  compare  nerve  fibers  to 
telegraph  wires,  and  nerve 
impulses  may  be  described  as  messages  that  pass  along  these  fibers. 
But  in  making  these  comparisons  we  must  remember  that  telegraphy 
and  the  action  of  the  nervous  system  have,  in  all  probability,  little  real 
resemblance.  We  know  that  nerves  transmit  impulses  at  the  rate  of 
about  one  hundred  feet  per  second ;  electricity  travels  thousands  of 
miles  per  second.  Hence  a  nerve  impulse  cannot  very  closely  re- 
semble what  we  call  a  telegraph  message.  On  the  other  hand,  this 
nerve  impulse  travels  much  too  rapidly  to  be  explained  as  a  chemi- 
cal or  mechanical  action.  We  must  therefore  admit  our  ignorance 
of  the  real  nature  of  the  nervous  impulse ;  nor  do  we  know  the  real 
nature  of  the  changes  that  take  place  in  the  nerve  cells  after  receiv- 


158  HUMAN  BIOLOGY 

ing  the  so-called  message.  The  principal  functions  of  the  brain 
may  for  convenience  be  divided  into  (1)  reflex  activities,  (2)  con- 
scious activities,  and  (3)  automatic  activities  or  habits. 

234.  Reflex  activities.  —  To  illustrate  the  reflex  action  of   the 
brain  suppose  we  inhale  some  pepper ;  a  message  goes  up  the  nerves 
to  the  cells  in  the  nerve  centers.     This  message  is  then  reflected  or 
switched  off  to  cells  which  send  impulses  down  the  nerves  that 
control  the  muscles  of  the  chest.     We  then  sneeze,  and  thus  get  rid 
of  the  pepper.     Coughing,  winking,  blushing,  the  flow  of  saliva  at 
the  sight  of  savory  food,  —  these  are  but  a  few  of  the.  reflex  activites 
carried  on  by  the  brain. 

235.  Conscious  activities.  —  As  long  as  we  keep  awake,  countless 
nerve  impulses  keep  pouring  into  our  brains.     When  the  cells  of  the 
gray  matter  receive  these  impressions,  we  usually  become  conscious 
that  we  are  seeing,  smelling,  hearing,  tasting,  or  feeling.     These 
sensations  are  more  or  less  lasting,  too,  for  we  can  recall  distinctly  the 
appearance  of  objects  that  we  saw  yesterday,  or  even  years  ago,  and 
we  can  hear  again,  as  it  were,  the  sounds  we  have  heard  in  the  past. 
In  some  unknown  way  these  impressions  are  stored  away  in  the 
protoplasm  of  the  brain,  and  constitute  our  memory. 

Another  power  of  which  we  are  conscious  is  the  ability  to  direct  the 
movements  of  the  body.  We  can  rise  from  a  seat,  walk  about,  talk 
or  change  the  expression  of  our  faces  as  we  will. 

236.  Habitual  activities.  —  If  we  can  remember  the  time  when  we 
learned  to  write,  we  recall  that  each  letter  was  traced  laboriously 
by  a  conscious  effort  of  our  brains  to  guide  the  muscles  of  our  fingers. 
Writing,  in  our  early  years,  belonged  to  the  group  of  our  conscious 
activities.     But  as  time  went  on,  less  and  less  of  our  attention  was 
needed  for  this  mechanical  process,  until  now  our  fingers  seem  to 
move  of  themselves.     Walking,  bicycle  riding,  swimming,  playing 
the  piano,  conveying  the  food  to  our  mouths  —  none  of  these  activi- 
ties require  our  attention.     We  have  made  these  movements  so 
many  times  that  they  have  become  automatic.     In  other  words,  the 
conscious  part  of  our  brains  has  trained  other  nerve  centers  to 


ADDITIONAL    TOPICS  IN  HUMAN  BIOLOGY       159 

direct  many  of  our  everyday  doings.     Our  attention  is  thus  set  free 
to  carry  on  other  kinds  of  work. 

"  As  every  one  knows,  it  takes  a  soldier  a  long  time  to  learn  his 
drill  —  for  instance,  to  put  himself  into  the  attitude  of  '  attention ' 
at  the  instant  the  word  of  command  is  heard.  But,  after  a  tune,  the 
sound  of  the  word  gives  rise  to  the  act,  whether  the  soldier  be  think- 
ing of  it,  or  not.  There  is  a  story,  which  is  credible  enough  though 
it  may  not  be  true,  of  a  practical  joker,  who,  seeing  a  discharged 
veteran  carrying  home  his  dinner,  suddenly  called  out  '  Attention  ! ' 
whereupon  the  man  instantly  brought  his  hands  down,  and  lost 
his  mutton  and  potatoes  in  the  gutter.  The  drill  had  been  thor- 
ough, and  its  effect  had  become  embodied  in  the  man's  nervous 
structure."1 

237.  Importance  of  habit.  —  The  tremendous  importance  of 
making  our  habits  our  allies  instead  of  our  enemies  cannot  be  em- 
phasized too  strongly. 

"  The  hell  to  be  endured  hereafter,"  says  Professor  James,  "  of 
which  theology  tells,  is  no  worse  than  the  hell  we  make  for  ourselves 
in  this  world  by  habitually  fashioning  our  characters  in  the  wrong 
way.  Could  the  young  but  realize  how  soon  they  will  become  mere 
walking  bundles  of  habits,  they  would  give  more  heed  to  their  con- 
duct while  in  the  plastic  state.  We  are  spinning  our  own  fates, 
good  or  evil,  and  never  to  be  undone.  Every  smallest  stroke  of 
virtue  or  of  vice  leaves  its  never-so-little  scar.  The  drunken  Rip 
Van  Winkle,  in  Jefferson's  play,  excuses  himself  for  every  fresh  dere- 
liction by  saying,  '  I  won't  count  this  tune! '  Wellf  he  may  not 
count  it,  and  a  kind  Heaven  may  not  count  it;  but  it  is  being 
counted,  none  the  less.  Down  among  his  nerve  cells  and  fibers  the 
molecules  are  counting  it,  registering  and  storing  it  up  to  be  used 
against  him  when  the  next  temptation  comes.  Nothing  we  ever 
do  is,  in  strict  scientific  literalness,  wiped  out.  Of  course  this  has 
its  good  side  as  well  as  its  bad  one.  As  we  become  permanent  drunk- 
ards by  so  many  separate  drinks,  so  we  become  saints  in  the  moral, 

1  Huxley's     "Lessons    in    Elementary  Physiology,"    Macmillan 
Company. 


160  HUMAN  BIOLOGY 

and  authorities  in  the  practical  and  scientific  spheres,  by  so  many 
separate  acts  and  hours  of  work.  Let  no  youth  have  any  anxiety 
about  the  upshot  of  his  education,  whatever  the  line  of  it  may  be. 
If  he  keep  faithfully  busy  each  hour  of  the  working  day,  he  may 
safely  leave  the  final  result  to  itself.  He  can  with  perfect  certainty 
count  on  waking  up  some  fine  morning,  to  find  himself  one  of  the 
competent  ones  of  his  generation,  in  whatever  pursuit  he  may  have 
singled  out." 

238.  Conditions  necessary  for  a  healthy  nervous  system.  —  In 
studying  the  hygiene  of  other  parts  of  the  body,  we  found  that  four 
conditions  were  necessary  for  healthy  activity.     That  the  nervous 
system,  too,  may  develop  as  it  should  and  that  it  may  do  its  work 
properly,  the  same  four  conditions  are  essential ;  namely,  food,  fresh 
air,  various  kinds  of  activity,  and  periods  of  rest. 

239.  Food  and  air. —  In  the  nervous  system  of  a  human  being  there 
are  millions  of  nerve  cells.     Each  of  these  cells  must  be  supplied  with 
nutritious  food  and  pure  air,  or  it  becomes  stunted  in  its  growth  and 
unable  to  do  its  proper  work.     These  busy  cells  are  constantly  giving 
off  carbon  dioxid,  water,  and  other  wastes,  and  if  these  are  not  re- 
moved and  fresh  oxygen  supplied,  one  feels  a  drowsiness  and  head- 
ache, and  is  unable  to  think  clearly.     Well- ventilated  rooms,  both 
by  day  and  by  night,  are  of  prime  importance  in  the  hygiene  of  the 
nervous  system. 

240.  Varied  activity.  —  To  develop  a  well-balanced    brain  one 
must  be  active  along  many  lines.     Experience  tells  us,  too,  that  we 
cannot  work  successfully  at  the  same  task  hour  after  hour  without 
some  change.     Hence,  varied  activity  is  an  important  principle  in 
sound  education.     The  young  child  must,  of  necessity,  turn,  after  a 
short  time,  from  one  lesson  to  another,  and  all  lessons  must  finally 
give  way  to  the  relaxation  of  play.     Unfortunate  is  the  boy  who  fails 
to  find  exhilaration  in  baseball,  bicycle  riding,  or  general  athletics, 
for  these  sports,  when  properly  regulated,  besides  developing  strong 
lungs  and  vigorous  muscles,  are  important  means  of  educating  the 
nerve  cells  and  fibers. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY        161 

Not  only  in  youth,  but  throughout  life,  must  the  student,  the 
business  man,  or  the  laborer,  at  the  end  of  a  day's  employment,  find 
relaxation  in  other  forms  of  activity.  If  he  fails  to  do  this,  not  only 
will  he  become  weary  of  his  work,  but  he  will  also  finally  come  to  lose 
the  power  of  enjoying  the  pleasures  he  has  been  neglecting.  In  the 
later  years  of  his  life,  the  great  naturalist,  Charles  Darwin,  wrote  as 
follows :  "  My  mind  seems  to  have  become  a  kind  of  machine  for 
grinding  general  laws  out  of  large  collections  of  facts.  ...  If  I  were 
to  live  my  life  again,  I  would  have  made  a  rule  to  read  some  poetry 
and  listen  to  some  music  at  least  once  every  week ;  for  perhaps  the 
parts  of  my  brain  now  atrophied  would  thus  have  been  kept  alive 
through  use.  The  loss  of  these  tastes  is  a  loss  of  happiness,  and 
may  possibly  be  injurious  to  the  intellect,  and  more  probably  to  the 
moral  character,  by  enfeebling  the  emotional  part  of  our  nature." 

241.  Rest.  —  Experiments  with  animals  show  a  striking  differ- 
ence in  the  appearance  of  nerve  cells  before  and  after  vigorous  exer- 
cise.    In  the  nerve  cells  of  a  bird  that  has  been  flying  all  day,  the 
protoplasm  has  a  distinctly  granular  appearance,  which  is  not  seen  in 
the  cells  before  exercise.    Tired  nerve  cells  can  be  restored  by  rest 
alone.     In  childhood  and  youth  an  abundance  of  sleep  is  absolutely 
essential  for  healthy  development.     Late  hours  of  evening  enter- 
tainment or  of  study  should  never  be  allowed  to  keep  growing  boys 
or  girls  from  having  at  least  nine  hours  of  sleep. 

242.  Effect  of  alcohol  on  the  nervous  system.  —  "  The  effect  of 
alcohol  appears  to  be,  as  it  were,  to  shave  off  the  nervous  system, 
layer  by  layer,  attacking  first  the  highest  developed  faculties  and 
leaving  the  lowest  to  the  last,  so  that  we  find  that  a  man's  judgment 
may  be  lessened,  though  at  the  same  time  some  lower  faculties,  such 
as  the  imagination  and  emotions,  may  appear  to  be  more  active  than 
before.  .  .  .    Thus  you  find  that  after  a  man  has  taken  alcohol  his 
judgment  may  be  diminished,  but  he  may  become  more  loquacious 
and  more  jolly  than  before.     Then  after  a  while  his  faculties  become 
dull;  he  gets  stupid  and  drowsy.  .  .  .     Later  on  it  affects  the  motor 
centers,  probably  the  cerebellum,  so  that  the  man  is  no  longer  able 
to  walk,  and  reels  whenever  he  makes  the  attempt.     At  this  tune, 

M 


162  HUMAN  BIOLOGY 

however,  he  may  still  be  able  to  ride  (on  horseback),  and  a  man  who 
is  so  drunk  that  he  cannot  walk  and  cannot  speak  may  ride  perfectly 
well.  .  .  .  Later  on  the  further  anaesthetic  action  of  the  alcohol 
abolishes  sensation,  and  its  paralyzing  action  destroys  the  power  of 
the  spinal  cord,  so  that  the  man  is  no  longer  able  even  to  ride ;  but 
still  the  respiratory  center  in  the  medulla  will  go  on  acting,  and  it  is 
not  until  enormous  doses  of  alcohol  have  been  given  that  respiration 
becomes  paralyzed. 

"  Alcohol  .  .  .  makes  all  the  nervous  processes  slower,  but  at  the 
same  time  it  has  the  curious  effect  of  producing  a  kind  of  mental 
anaesthesia,  ...  so  that  these  processes  seem  to  the  person  himself 
to  be  all  quicker  than  usual,  instead  of  being,  as  they  really  are,  much 
slower.  Thus  a  man,  while  doing  things  much  more  slowly  than 
before,  is  under  the  impression  that  he  is  doing  things  very  much 
more  quickly.  What  applies  to  these  very  simple  processes  applies 
also  to  the  higher  processes  of  the  mind ;  and  a  celebrated  author 
once  told  me  that  if  he  wrote  under  the  influence  of  a  small  quantity 
of  alcohol,  he  seemed  to  himself  to  write  very  fluently  and  to  write 
very  well,  but  when  he  came  to  examine  what  he  had  written  next 
day,  after  the  effect  of  the  alcohol  had  passed  off,  he  found  that  it 
would  not  stand  criticism."  1 

V.  THE  EYES 

243.  Protection  for  the  eye.  —  The  delicate  organs  of  vision,  the 
eyes,  are  protected  in  a  wonderful  manner.     In  the  first  place,  the 
eyeballs  are  set  far  back  in  bony  sockets,  in  such  a  way  that,  even 
if  one  falls  forward  or  if  the  face  is  struck  with  a  large  object,  there  is 
little  danger  that  the  eyes  themselves  will  be  hit.     Again,  each  eye- 
ball is  covered  by  two  movable  lids  that  involuntarily  close  at  any 
threatened  danger.     And,  finally,  the  curving  eyelashes  on  the  edge 
of  each  lid  protect  the  eyeball  to  a  considerable  extent  from  dust 
and  dirt. 

244.  Structure  of   the ,  eye.  —  Each  eye  is  nearly  spherical  in 
shape  (Fig.  52) .     Its  outer  surface  is  covered  with  a  tough  coat  which 

1  T.  Lauder  Brunton,  London,  "Lectures  on  the  Action  of  Medi- 
cine," pp.  190,  191,  194. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY       163 


is  white  in  color,  except  in  front,  where  it  becomes  the  transparent 

cornea. 

Inside  of  the  outer  coat  is  a  second  layer  which  is  seen  beneath 

the  cornea  as  a  colored  ring  known  as  the  iris.     In  the  center  of  the 

iris  is  a  circular  opening,  the  pupil,  which  is  black  hi  appearance. 

Through  the  pupil  enter  the  rays  of  light  into  the  interior  of  the 

eyeball.     If  one  comes  suddenly  from  a  dark  room  into  the  light,  it 

is    possible    to    see    this    opening 

quickly  decrease  in  size.     The  inner 

lining  of  the  eyeball  is  extremely 

thin  and  black  in  color ;  it  is  known 

as  the  retina,  and  connected  with 

it  are  the  many  nerve  fibers  that 

carry  messages  to  the  brain. 

Behind   the   iris   is   a  beautiful 

transparent  object,  the  crystalline 
lens,  both  surfaces  of  which  are 
convex.  The  space  within  the  eye- 
ball in  front  of  this  lens  is  occupied 
by  a  liquid,  and  behind  the  lens  is 
a  jellylike  substance. 

FIG.  52.  —  Section  of  the  eye. 
246.  The  eye  as  a  camera.  — 
Any  one  who  is  at  all  familiar  with 
a  camera  knows  that  by  means  of 
a  lens,  gr  a  combination  of  lenses, 
the  scene  to  be  photographed  is 
made  to  appear  upside  down  on  the  ground  glass  plate  at  the  back 
of  the  camera.  If  the  image  is  not  clear,  it  is  brought  into  focus 
by  moving  the  lens  nearer  to,  or  farther  from,  the  object. 

In  the  eye,  too,  we  have  an  arrangement  similar  to  that  of  a 
camera,  since  the  convex  surfaces  of  the  cornea  and  crystalline  lens 
(Fig.  53)  focus  the  rays  of  light  so  that  an  image  is  formed  on  the 
sensitive  retina  at  the  back  of  the  eye.  Since,  however,  the  lenses 
within  the  eye  cannot  be  moved  backwards  and  forwards,  as  in  a 
camera,  focusing  or  accommodation  of  the  eye  must  be  accomplished 


C  =  Cornea. 
I  =  Iris. 

L  =  Crystalline  lens. 
ON  =  Optic  nerve. 

R  =  Retina. 
V.  H.  =  Jellylike  substance. 


164 


HUMAN  BIOLOGY 


in  a  different  way,  namely,  by  making  the  elastic  lens  more  or  less 
convex. 

246.  Sensations  of  sight.  —  We  shall  now  try  to  see  how  it  is  that 
the  eye  helps  us  to  get  sensations  of  sight.  If  an  object,  say  an 
arrow,  is  held  in  front  of  the  eye,  rays  of  light  pass  in  a  great  many 
directions  from  every  part  of  the  arrow  tip.  A  considerable  number 
of  these  rays  strike  the  convex  surface  of  the  cornea  and  the  crystal- 
line lens,  and  are  thereby  focused,  or  made  to  converge  upon  a  point 
on  the  retina.  In  the  same  way  the  light  rays  from  every  other  part 
of  the  arrow  are  brought  to  focus  on  the  inner  surface  of  the  retina. 
By  this  means  a  smaller,  inverted  image,  of  the  arrow  (Fig.  53)  is 


FIG.  53.  —  Formation  of  an  image  on  the  retina. 

projected  on  the  inner  lining  of  the  eye.  The  influence  of  these  light 
rays  then  passes  through  the  layers  of  the  retina,  and  when  these 
so-called  "  messages  "  traverse  the  nerve  fibers  and  reach  the  brain, 
we  become  conscious  of  sensations  of  sight. 

247.  Defective  eyes.  —  A  normal,  healthy  eye  has  the  power  of 
adjusting  itself  so  that  objects  become  visible  which  are  within  five 
to  ten  inches,  or  as  far  away  as  a  distant  horizon.  Many  people, 
however,  find  that  they  can  see  objects  near  at  hand  much 
more  clearly  than  those  at  a  distance;  in  other  words,  they  are 
nearsighted.  Others,  on  the  other  hard,  are  farsighted.  These 
defects  in  vision  are  due  to  imperfect  formation  of  the  eye,  and  can 
be  corrected  only  by  the  use  of  proper  eyeglasses  or  spectacles,  which 
should  be  purchased  only  on  the  recommendation  of  a  competent  eye 
specialist. 

Another  very  common  defect  of  the  eye  is  known  as  a-stig'- 
ma-tism.  Many  people,  on  looking  with  each  eye  separately  at 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY       165 

Figure  54,  find  that  some  of  the  radiating  lines  stand  out  sharply  de- 
fined, while  others  are  indistinct  or  blurred.  In  reality,  all  the  lines 
are  equally  distant  from  each  other,  and  the  indistinctness  referred 
to  above  is  due  to  the  fact  that  some  of  the  rays  of  light  are  not 
brought  to  a  focus.  Astigmatism,  like  nearsightedness  and  far- 
sightedness, should  be  corrected  by  the  use  of  proper  glasses,  other- 
wise constant  eyestrain  is  likely  to 
cause  headaches  and  other  disorders 
of  the  body. 

Some  people,  too,  are  unable  to  dis- 
tinguish clearly  various  colors;  thus, 
red  and  green  may  appear  the  same  to 
them.  In  other  words,  such  people 
are  color  blind.  Color  blindness  can- 
not be  corrected  by  glasses,  but  may 
be  to  some  extent  by  training. 

rp,,       FIG.  54.  —  Test  for  astigmatism. 
248.    Hygiene  of  the  eyes.  —  The 

eyes  have,  as  we  know,  wonderful  powers  of  adapting  themselves  to 
varying  conditions.  This  adaptability  often  leads  us  to  abuse  them. 
Thus,  we  frequently  read  when  the  light  is  insufficient,  we  look 
steadily  at  objects  until  we  suddenly  find  that  we  cannot  see 
clearly,  and  we  read  or  study  while  riding  in  swiftly  moving  trains. 
In  these  and  other  ways  we  compel  our  eyes  to  make  adjustments 
under  trying  conditions,  and  more  or  less  eyestrain  is  sure  to 
follow. 

When  we  read,  we  should  make  sure  that  the  light  is  sufficient, 
that  it  is  steady,  and  that  it  comes  over  the  left  shoulder.  The  type 
on  the  printed  page  should  be  little,  if  any,  smaller  than  that  in  which 
most  of  this  book  is  printed,  the  lines  should  not  be  close  together, 
and  the  paper  should  not  have  a  glossy  surface  to  reflect  the  light 
into  the  eyes.  One  should  remember,  too,  that  the  eyes,  like  other 
organs  of  the  body,  need  frequent  periods  of  rest.  Hence  study 
hours  should  be  followed  by  periods  in  which  the  eyes  are  allowed  to 
relax.  Pupils  who  have  defective  eyesight  should  at  once  secure 
proper  glasses. 


166 


HUMAN  BIOLOGY 


VI.   THE  EAR 

249.  The  external  ear.  —  Attached  to  each  side  of  the  head  is 
an  oval,  more  or  less  flattened  expansion,  composed  largely  of  car- 
tilage and  connective  tissue.  The  irregular  surface  of  this  outer 
portion  of  the  ear  doubtless  helps  somewhat,  like  an  ear  trumpet,  to 
catch  and  converge  the  sound  waves  into  the  funnel-like  canal 
which  is  about  an  inch  long,  and  leads  to  the  interior  of  the  head. 


The  Hammer 


The .  Loops 
(Semicircular 
Canals). 


The  Anvil .  The  Stirrup 

Eustachian  Tube. 
FIG.  55.  —  Middle  and  inner  ear,  greatly  enlarged. 

In  the  lining  of  this  canal  are  certain  wax  glands;  these  secrete 
a  thin  fluid  which,  on  thickening,  hardens  into  a  yellow  paste,  the 
earwax.  Across  the  inner  end  of  this  tube  of  the  external  ear  is 
stretched  a  thin  membranous  partition,  known  as  the  eardrum,  or 
tym'pa-num  (Latin  tympanum  =  drum  (Fig.  55)). 

It  is  never  safe  for  one  to  thrust  into  the  canal  of  the  ear  any  hard 
object,  because  of  the  danger  of  puncturing  the  eardrum.  Ordina- 
rily the  canal  cleans  itself,  but  if  it  is  necessary  to  remove  bits  of 
wax  or  dirt,  this  should  be  done  with  a  tightly  rolled  corner  of  a  piece 
of  cloth.  It  is  dangerous,  too,  to  punish  a  child  by  boxing  the  ears, 


ADDITIONAL    TOPICS  IN  HUMAN  BIOLOGY       167 

because  the  sudden  compression  of  the  air  is  likely  to  injure  the  drum. 
Earache  is  often  relieved  by  hot  applications ;  never  should  lauda- 
num or  other  substances  be  put  into  the  ear  without  the  advice  of 
a  physician. 

250.  The  middle  ear.  —  Beyond  the  tympanum  is  a  small  cav- 
ity, known  as  the  middle  ear.     From  this  cavity  a  narrow  tube 
(the  Eustachian  tube)  about  an  inch  and  a  half  long,  communicates 
with  the  upper  part  of  the  throat  cavity  (Fig.  55).     If  one  were  to 
go  up  on  a  high  mountain,  he  would  find  that  the  pressure  of  the 
air  on  the  outside  of  the  body,  and  therefore  on  the  exterior  of 
the  eardrum,  would  become  less,  and  if  some  of  the  air  in  the  middle 
ear  were  not  to  escape,  the  eardrums  would  be  forced  outward,  and 
hence  would  be  ruptured.     If,  on  the  other  hand,  one  should  go  into 
a  deep  mine,  the  increased  pressure  on  the  outside  of  the  drums 
would  force  them  inward.    All  these  accidents  are  prevented  by  the 
presence  of  the  Eustachian  tubes,  through  which  air  can  pass  into 
and  out  from  the  middle  ear,  and  so  the  pressure  on  both  sides  of 
the  tympanum  can  be  equalized.     In  severe  head  colds,  the  opening 
from  the  throat  cavity  into  the  Eustachian  tubes  becomes  tempo- 
rarily closed  and  we  are  then  conscious  of  a  ringing  sensation  in  the 
ears.     Catarrh  sometimes  closes  the  Eustachian  openings  and  causes 
deafness.     If  the  hearing  seems  to  be  at  fault  in  any  way,  a  specialist 
should  be  consulted. 

251.  Sensations  of  sound.  —  When  a  stone  is  dropped  into  water, 
the  ripples  move  outward  over  the  surface  in  circular  waves.     In  a 
similar  manner  sound  waves  are  transmitted  in  all  directions  from 
a  given  body,  for  instance,  a  vibrating  bell.     When  some  of  these 
sound  waves  enter  the  tube  of  the  external  ear,  they  cause  the  ear- 
drum to  vibrate,  and  this  vibration  is  transmitted  across  the  middle 
ear  by  a  chain  of  tiny  bones,  and  so  reaches  the  complicated  inner  ear, 
which  is  a  series  of  canals  imbedded  in  solid  bone.     The  inner  ear- 
contains  a  large  number  of  sensitive  cells  which  transfer  the  vibra- 
tions to  nerves  communicating  with  the  brain.     When  the  brain 
cells  receive  and  interpret  these  impulses,  we  get  sensations  of 
sound. 


168  HUMAN    BIOLOGY 

GREAT  BIOLOGISTS 

252.  Library  studies  of  biologists.  —  Select  for  study  one  or  more 
of  the  following  men  who  have  made  great  contributions  to  our 
knowledge  of  biology :  Agassiz,  Aristotle,  Audubon,  Darwin,  Harvey, 
Huxley,  Jenner,  Koch,  Lamarck,  Leeuwenhoek,  Linnseus,  Lister, 
Pasteur,  Spencer,  Wallace.  Consult  Locy's  "Biology  and  its 
Makers,"  Williams's  "A  History  of  Science/'  Encyclopedias  or 
other  works  of  reference  as  to  (1)  the  important  events  in  the  life 
of  the  biologist,  and  (2)  his  contributions  to  biological  science. 

Louis  PASTEUR1  (See  Frontispiece) 

I.  Interesting  Features  of  his  Biography. 

1.  Parents. 

a.  Father   (Jean   Joseph),   a  tanner  —  sergeant  major    in 

Napoleon's  army  —  decorated  with  Legion  of  Honor. 

b.  Mother  (Jeanne  Rogui)  of  middle  class  family. 

2.  Birth,  at  Dole  (in  Eastern  France),  Dec.  27,  1822. 

3.  Education. 

a.  In  colleges  near  his  birthplace  (Arbois  and  Besanc,on) 

—  early  evidences  of  remarkable  ability  in  concentrat- 
ing his  mind  in  study. 

b.  In  colleges  at  Paris  —  much  influenced  by  the  scientists 

Dumas  and  Biot. 

1  The  ability  to  prepare  logical  outlines  of  library  or  laboratory 
studies  is  of  great  value  to  students  (1)  because  in  this  form  the 
principal  facts  can  be  stated  more  briefly  than  is  possible  in  con- 
tinuous paragraphs,  and  (2)  because  the  various  interrelations  of 
the  facts  may  be  more  clearly  shown.  In  preparing  such  out- 
lines the  student  should  first  select  the  most  important  division 
topics,  all  of  which  should  be  of  equal  value  and  expressed  in  similar 
form.  Each  of  the  various  subordinate  topics  should  be  an  organic 
part  of  the  main  division  topic  under  which  it  is  placed  ;  each  should 
be  stated  in  a  brief  form,  and  as  far  as  possible  words  or  phrases 
should  be  used  and  verbs,  clauses,  or  sentences  avoided. 

The  outline  on  the  life  and  works  of  Louis  Pasteur  is  inserted 
(1)  because  of  the  importance  of  Pasteur's  work,  and  (2)  as  a  sug- 
gestive form  for  biology  records. 


ADDITIONAL   TOPICS  IN  HUMAN  BIOLOGY        169 

4.  Professional  work. 

a.  Professor  of  Physics  at  Dijon  (1848),  and  of  Chemistry 

at  Strassburg  (1849). 
6.  Professor  and  Dean  of  Faculty  at  Lille  (1854). 

c.  Scientific  Director  of  Ecole  Normale,  Paris  (1847),  and 

Professor  of  Chemistry  at  Sorbonne,  Paris  (1867). 

d.  Director  of  Pasteur  Institute,  Paris  (1888). 

5.  Death,  at  St.  Cloud,  Sept.  28,  1895. 

6.  Position  as  a  scientist. 

a.  His  life  devoted  to  most  important  scientific  investi- 

gations. 

b.  Highest  honors  bestowed  upon  him  by  men  of  science  in 

all  countries. 

c.  "The  most  perfect  man  in  the  realm  of  science." 
II.   Important  Contributions  to  Biological  Knowledge. 

1.  Investigations  relative  to  fermentation  and  decay. 

a.  Fermentation  formerly  believed  to  be  purely  a  chemical 
process,  independent  of  the  activity  of  living  organ- 
isms. 

6.  Fermentation  and  putrefaction  proved  by  Pasteur  to 
be  always  due  to  the  action  of  living  microorganisms 
(yeast  and  bacteria). 

c.  Each  kind  of  fermentation  or  decay  demonstrated  to  be 
due  to  the  activity  of  different  lands  of  germs. 

2.  Discoveries  relative  to  silkworm  disease. 

a.  Silk  cultivation  throughout  France  and  Italy  threatened 

by  this  disease. 

b.  Silkworm    disease    proved    by    long    investigations    of 

Pasteur  to  be  due  to  minute  germs  infesting  eggs, 
larvae,  pupae,  and  moth  of  silkworm. 

c.  Disease  eradicated  by  scientific  treatment  suggested  by 

Pasteur. 

3.  Researches  relative  to  splenic  fever  among  horses,  cattle,  sheep, 

and  human  beings. 

'a.  Rod-shaped  bacteria  found  to  be  the  cause  of  the  disease. 
b.  Bacteria  from  the  bodies  of  buried  victims  of  the  disease 


170  HUMAN  BIOLOGY 

proved  by  Pasteur  to  be  brought  to  the  surface  by 
earthworms. 

c.  Splenic  fever  checked  by  inoculating  animals  with  a 
virus  prepared  in  a  manner  somewhat  like  that  of  the 
virus  of  hydrophobia  (see  4  below). 
4.  Discoveries  relating  to  hydrophobia  (1885}. 

a.  Hydrophobia  demonstrated  to  be  a  disease  attacking  the 

nervous  system  of  victims  bitten  by  mad  dogs,  wolves, 
or  cats. 

b.  Solutions  made  from  fresh  spinal  cords  of  animals  thus 

bitten,  on  being  injected  into  healthy  animals  always 
cause  hydrophobia. 

c.  Spinal  cords  of  animals  dying  of  hydrophobia  found  to 

lose    virulence    (i.e.    disease-producing   power)    after 
being  dried. 

d.  Virus    (i.e.   glycerine   solutions)    obtained   from   spinal 

cords  dried  for  varying. lengths  of  time  found  to  con- 
tain corresponding  degrees  of  virulence. 

e.  Method  of  treatment  for  hydrophobia. 

(a)  Cauterization    (burning)    of    wound  with  strong 

nitric  acid. 
(6)  Injection  on  twenty-one  successive  days  of  virus 

of  gradually  increasing  strength. 

/.  Result  of  Pasteur  treatment  in  Paris;    of  21,631  cases 
treated  only  99  victims  of  the  disease  died,  i.e.  less  than 
1  per  cent. 
5.  Discoveries  of  other  scientists  directly  due  to  Pasteur's  work. 

a.  Lister's  methods  of  antiseptic  treatment  of  wounds. 

b.  Koch's  investigations  as  to  the  cause  and  treatment  of 

tuberculosis. 

c.  Roux's  and  von  Behring's  antitoxin  treatment  for  diph- 

theria. 


APPENDIX  I 

LABORATORY  EQUIPMENT 

The  laboratory.  —  It  is  very  desirable  that  a  definite  room  or 
rooms  be  set  apart  for  work  in  biology,  since  at  least  a  minimum 
equipment  is  essential,  and  this  cannot  be  transferred  from  room 
to  room  without  considerable  loss  of  efficiency.  While  it  is  desirable 
to  have  tables  or  at  least  flat-topped  desks  of  good  size,  satisfactory 


FHDNT   ZLEYATTDN. 


END   ELEVATION- 


TOP. 

FIG.  87.  —  Plans  for  a  laboratory  table. 

laboratory  work  can  be  done  in  an  ordinary  class  room  if  it  is  well 
lighted.  The  laboratory  should  be  supplied  with  a  demonstration 
table  and  gas  connection  if  possible,  with  sink  and  running  water, 
and  a  broad  shelf  should  be  placed  in  front  of  the  windows  for  sup- 
porting growing  plants  and  aquaria,  and  for  use  in  demonstrations 
with  the  compound  microscope.  Ample  closet  room  should  be  pro- 
vided in  which  to  store  apparatus  and  supplies,  so  that  they  may  be 
kept  free  from  dust. 

171 


172  APPENDIX  I 

In  case  it  is  possible  to  equip  a  room  with  laboratory  tables  the 
following  type  is  suggested.  In  the  first  place  the  laboratory  tables 
should  be  firmly  fixed  to  the  floor,  and  arranged  so  that  the  light 
comes  from  the  left  side,  and  if  possible  also  from  the  back  of  the 
room.  The  desk  tops  should  be  30  inches  from  the  floor  and  20 
inches  wide,  and  should  be  made  of  maple  or  other  hard  wood.  The 
length  of  each  table  will  of  course  depend  upon  the  dimensions  of 
the  room,  but  if  possible  no  more  than  three  pupils  should  be  pro- 
vided for  at  a  single  table.  Each  student  should  have  at  least 
30  inches  of  the  table  space.  (Fig.  87.) 

"  The  finish  of  the  laboratory  table  tops  is  a  matter  of  importance, 
since  it  must  be  such  as  to  protect  the  wood  from  damage,  and  keep 
it  clean  and  smooth.  Many  prefer  a  black  finish,  to  obtain  which  the 
following  method  gives  good  results. 

"  Make  up  solutions : 

(1)  Copper  sulphate  (CuS04)       .     .     .  625  grams 
Potassium  chlorate  (KC10  )  .     .     .  625  grams 
Water  to  make     .     .    .    .    .  -,     .  5  liters 

(2)  Anilin  oil 300  grams 

Hydrochloric  acid  (HC1)    .    „    .    .  450  grams 

Water  to  make 5  liters 

"  Apply  solution  (1),  followed  immediately  by  (2)  several  times, 
until  the  wood  becomes  a  dark  green,  allowing  the  applications  to 
dry  each  time.  The  darker  the  tone  reached,  the  better.  The 
wood  must  then  be  washed  thoroughly  with  soap  and  hot  water 
applied  with  a  brush.  This  is  necessary  in  order  to  remove  the  super- 
fluous salts.  The  table  is  finished  with  oil  and  will  then  be  dead 
black."1 

The  advantages  of  the  dull  black  finish  are  these:  (1)  there  is 
little  reflection  of  light  from  this  kind  of  surface  into  the  eyes  of  the 
pupils;  (2)  the  black  surface  furnishes  an  admirable  background 
for  many  objects  of  study ;  and  (3)  the  tops  are  not  injured  by  water, 
acids,  or  other  chemicals. 

Experience  has  shown  that  unless  the  laboratory  must  be  used 

1  From  Lloyd  and  Bigelow's  "The  Teaching  of  Biology." 


APPENDIX  I  173 

as  an  assembly  room  for  a  division  at  the  beginning  and  close  of 
school,  drawers  and  shelves  beneath  the  desk  are  of  little  real  use, 
and  often  become  mere  receptacles  for  laboratory  debris,  unless 
they  are  provided  with  locks.  It  is  usually  far  safer  and  more  satis- 
factory to  collect  drawings,  magnifiers,  pencils,  etc.,  at  the  close 
of  the  period,  and  to  distribute  materials  as  they  are  needed  during 
the  next  period.  If  this  work  is  properly  systematized  and  the 
assistance  of  pupils  is  made  use  of,  very  little  of  the  laboratory 
time  is  lost  hi  this  way. 

Seats  fixed  to  the  floor,  likewise,  are  of  great  advantage.  The 
authors  have  found  that  the  best  seat  for  this  purpose  is  the  Chandler 
chair,  which  is  furnished  by  the  American  Seating  Company, 
19  West  18th  St.,  New  York  City.  It  has  a  strong  iron  base,  which 
can  be  screwed  to  the  floor,  and  the  chair  seat  turns  on  ball-bear- 
ings through  an  arc  of  180  degrees.  The  price  of  the  chair  is  $2. 

Apparatus  and  chemicals.  —  The  following  lists  of  apparatus 
and  chemicals  are  suggested  as  a  minimum  equipment  for  a  class 
of  24.  Most  of  the  items  can  be  purchased  from  any  one  of  the  fol- 
lowing dealers : 

Bausch  and  Lomb  Optical  Co.,  Rochester,  New  York. 
Kny-Scheerer  Co.,  404  West  27th  St.,  New  York  City. 
0.  T.  Louis,  59  Fifth  Avenue,  New  York  City. 

QUANTITY          APPARATUS  AND  GLASSWARE  ESTIMATED  PRICE 

1        Compound  microscope,  with  |-  and  |-inch  objec- 
tives, double  nose-piece,    1  inch    eye-piece,  and 

revolving  disk-diaphragm $30.00 

24       Magnifiers,  doublets,  1^-inch  focus 16.20 

1        Harvard  trip-scale  balance        6.00 

12       Evaporating  dishes,  3  niches  diameter 1.50 

1  2-quart  agate  double  boiler 1.50 

2  Alcohol  lamps  or         .50 

2  Bunsen  burners  (if  gas  is  available) .40 

3  ft.  Rubber  tubing  (heavy)  to  fit  Bunsen  burners     .     .          .60 
144       Slides,  plain,  1X3  inches 80 


174  APPENDIX  I 

1  oz,  Cover  glasses  (round) $   .70 

12        Sloyd  knives 2.25 

24  Forceps  (heavy) 5.00 

12        Dissecting  scissors 2.25 

50        Handles  (adjustable)  for  dissecting  needles    .     ,     .  2.00 

100       Needles  for  handles         25 

144        6-inch  test  tubes 1.50 

12        8-inch  test  tubes,  hard  glass 1.50 

2  Chemical  thermometers  (Fahrenheit  and  Centigrade 

scale  on  same) 2.00 

1        Lactometer        .50 

1  Radiometer 1.10 

2  Iron  ring-stands  (3  rings) 1.10 

2       Pieces  wire  gauze  (4X4  inches) .08 

2  Pieces  asbestos  (4X4  inches) .07 

6        Glass  stirring  rods .10 

25  ft.  Glass  tubing,  5  mm.  outside .30 

10  ft.  Rubber  tubing  to  fit  glass  tubing .70 

12       Thistle  tubes  (medium  size) 1.00 

12       Beakers,  150  to  250  cc 1.50 

3  Bell  jars  2  feet  high  and  10  inches  in  diameter   .     .  14.40 
3       Bell  jars  about  8  inches  high  and  10  inches  in  diam- 
eter        5.00 

1       Bell  jar,  open  top,  8  inches  high  and  8  inches  in 

diameter 2.00 

1  piece  Sheet  rubber  2  feet  square  (should  be  kept  in 

lightning  fruit  jar  when  not  in  use) 1.50 

24        Lightning  fruit  jars  (1  quart) 3.00 

6       Flasks,  250  cc 1.00 

36        Petri  dishes,  4  inches  in  diameter 6.00 

1        Cylindrical  graduate,  1000  cc 1.35 

1        Cylindrical  graduate,  100  cc .40 

6       TaU  glass  cylinders  (1000  cc.)       1.75 

1        Box  slide  labels 10 

1       Box  labels,  2x3  inches 18 

1       Steam  sterilizer,  copper  bottom,  18  inches  high  .    .  6.00 


APPENDIX  I  175 

50       8-ounce  wide-mouthed  bottles «  $2.20 

50       4-ounce  wide-mouthed  bottles      ...     .     .     .    .  1.60 

24       200  cc.  narrow-mouthed  bottles  with  ground  glass 

stoppers 2.60 

100       Vials  with  corks,  3  inches  high,  1  inch  in  diameter    .  2.75 

100       Corks  to  fit  8-ounce  wide-mouthed  bottles     .     .    .  1.00 

100       Corks  to  fit  4-ounce  wide-mouthed  bottles     ...  .75 

100       Corks  to  fit  6-inch  test  tubes .40 

10       Rubber  stoppers  with  2  holes  to  fit  250-cc.  flasks  .    .  .45 

10  Rubber  stoppers  with  1  hole  to  fit  6-inch  test  tubes    .  .30 
2       Insect  spreading  boards *    .    .  1.00 

QUANTITY          CHARTS  AND  PREPARATIONS          ESTIMATED  PRICE 

11  Jung  plant  charts    (pansy,  horse-chestnut,   tulip, 

linden,  potato,  carrot,  pea,  Spirogyra,  mold,  fern, 

moss) $13.20 

1        Teachers'  Botanical  Aid,  28  charts,  containing  300 
drawings  (Western  Publishing  House,  Chicago, 

HI.). 12.50 

11  Jung  animal  charts  (fish  (external),  fish  (internal), 
frog,  Amoeba,  Paramecium,  crayfish,  bee,  but- 
terfly, cricket,  finch,  duck) 13.20 

4       Leuckhart  animal  charts  (grasshopper,  bee,  -butter- 
fly, metamorphosis  of  frog) 8.00 

1       Model   of   heart   and  lungs    (dissectible),  natural 

size       12.75 

1       Model  of  digestive  system  on  panel,  natural  size      .  15.75 

1        Model  of  circulatory  system  on  panel,  natural  size   .  11.75 

1       Articulated  human  skeleton,  clutch  standard  .     .     .  35.00 

1       Life  history  of  butterfly 6.00 

1        Life  history  of  honey  bee 5.00 

1        Life  history  of  frog 5.00 

1        Life  history  of  fish 5.00 

1        Half  skeleton  of  fish  (glass  case)  .    .    .....    .    .    .  3.00 

1       Half  skeleton  of  frog  (glass  case) 4.00 


176  APPENDIX  I 

8  Microscopical  slides  of  plant  tissue  (cross  section 
and  longitudinal  section  of  young  root,  cross 
section  and  longitudinal  section  of  stem  one  year 
old,  cross  section  of  hydrangea  leaf,  epidermis 
of  leaf,  separate  wood  cells,  ducts,  conjugating 

Spirogyra) $3.50 

5  Microscopical  slides  of  animals  (Amoeba,  Para- 
mecium,  frog's  blood,  human  blood,  mouth  parts 

of  bee) 3.00 

QUANTITY                  LIST  OF  CHEMICALS                  ESTIMATED  PRICE 

2  Ib.        Hydrochloric  acid $1.00 

1  Ib.        Nitric  acid     .     .   v .28 

1  Ib.        Ammonia »  .26 

1  oz.       Iodine .30 

5  oz.       Potassium  iodide .90 

lib.        Ether 40 

1  Ib.        Caustic  soda       .30 

1             Small  tube  red  litmus  paper .08 

1             Small  tube  blue  litmus  paper .08 

1  gal.      95  per  cent  alcohol 3.50 

10  Ib.        40  per  cent  formalin 1.70 

8  oz.       Glycerin .25 

1  oz.        Pepsin 30 

lib.        Peptone 2.00 

1  oz.        Taka  diastase 1.70 

1  Ib.        Salt       .05 

1  oz.       Phosphate  of  lime .12 

1  Ib.        Grape  sugar .12 

£  Ib.        Cooking  soda .10 

1  Ib.        Copper  sulphate .35 

1  Ib.        Rochelle  salt       .     . « 30 

1  jar       Beef  extract 75 

lib.        Agar 90 

|  Ib.        Powdered  sulphur        .07 

1  Ib.        Potassium  chlorate  .20 


APPENDIX  I  177 

|  Ib.  Manganese  dioxid       . $.35 

1  Ib.  Granulated  zinc      .....< .25 

1  Ib.  Absorbent  cotton .35 

6  Small  candles .10 

1  Ib.  Marble  pieces .10 

5  Ib.  Plaster  of  Paris 10 

5  oz.  Potassium  cyanide .10 

1  oz.  Ferric  chloride .05 

1  Ib.  Corn  starch .10 

^  Ib.  Arrow  root  starch .15 

1  oz.  White  egg  albumen .12 

1  oz.  Powdered  carmine .40 

1  oz.  Gluten  .15 


APPENDIX   II 

ORDER  OF  TOPICS 

The  following  order  of  topics,  with  time  assignment  for  each,  has 
been  found  by  the  authors  to  be  satisfactory: 

I.  Course  begun  in  September  and  completed  in  June. 

1.  The  general  structure  of  plants  (organs  of  a  plant)      2  lessons 

2.  Reproduction  in  plants. 

o.  Structure  and  adaptations  of  flowers      ...     15  lessons 
b.  Structure  and  adaptations  of  fruits,  including 

fruit  and  seed  dispersal 5  lessons 

3.  Plant  propagation. 

a.  Seeds  and  their  development  into  plants    .     .      6  lessons 

b.  Conditions  essential  for  the  growth  of  plants  .      2  lessons 

4.  Cellular  structure  of  plants,  including  fertilization 

of  flowers 5  lessons 

5.  Composition  of  living  and  lifeless  things. 

a.  Elements,  compounds,  oxidation,  with  defini- 

tions  10  lessons 

b.  Composition  of  food  substances,  with  tests  for 

each       8  lessons 

c.  Manufacture  of  food  substances  by  plants  .     .  5  lessons 

6.  Osmosis  and  digestion 5  lessons 

7.  Adaptations  of  the  nutritive  organs  of  plants. 

a.  Structure  and  adaptations  of  roots    ....      5  lessons 

b.  Structure  and  adaptations  of  stems   ....      3  lessons 

c.  Structure  and  adaptations  of  leaves  ....      4  lessons 

8.  Respiration  and  the  production  of  energy  in  plants  4  lessons 

9.  Plants  in  their  relation  to  human  welfare. 

178 


APPENDIX  II  179 

a.  Some  uses  of  plants  to  man 3  lessons 

6.  Forests  and  forest  conservation 3  lessons 

10.  Single-celled  animals   .     .    '.    .    *    . \ .    .    .     .  5  lessons 

11.  Fish  (and  frog,  if  this  form  is  taught)  '.    .^  '.    .  14  lessons 

12.  The  general  structure  of  the  human  body  ...  3  lessons 

13.  Microorganisms  and  their  relation  to  human  wel- 

fare.    ...    . 10  lessons 

14.  Nutrients  and  their  uses 7  lessons 

15.  Stimulants,  narcotics,  and  poisons 10  lessons 

16.  Digestion  of  the  nutrients 7  lessons 

17.  Circulation  of  the  nutrients      .    .    ~? •-.    ."..•*.  6 lessons 

18.  Respiration  and  the  production  of  heat  and  power 

in  man 7  lessons 

19.  Additional  topics  in  hygiene 9  lessons 

20.  Birds 5  lessons 

21.  Insects 15  lessons 

II.  Course  begun  in  February  and  completed  in  January. 

1.  Composition  of  living  and  lifeless  things. 

a.  Elements,  compounds,  oxidation,  with  defini- 
tions    10  lessons 

6.  Composition  of  food  substances,  with  test  for 

each 8  lessons 

c.  Manufacture  of  food  substances  by  plants    .  5  lessons 

2.  General  structure  of  plants,  including  cellular 

structure 5  lessons 

3.  Osmosis  and  digestion 5  lessons 

4.  Adaptations  of  the  nutritive  organs  of  plants. 

a.  Structure  and  adaptations  of  roots  ....  5  lessons 

6.  Structure  and  adaptations  of  stems      ...  3  lessons 

c.  Structure  and  adaptations  of  leaves      ...  4  lessons 

5.  Respiration  and  the  production  of  energy  in  plants  4  lessons 

6.  Reproduction  in  plants. 

a.  Structure  and  adaptations  of  flowers    ...  15  lessons 
6.  Structure  and  adaptations  of  fruits,  including 

fruit  and  seed  dispersal 5  lessons 


180  APPENDIX  II 

7.  Plant  propagation. 

a.  Seeds  and  their  development  into  plants  .     .  6  lessons 

b.  Conditions  essential  for  the  growth  of  plants  .  2  lessons 

8.  Plants  in  their  relation  to  human  welfare. 

a.  Some  uses  of  plants  to  man    ......  3  lessons 

b.  Forests  and  forest  conservation 3  lessons 

9.  Insects .  15  lessons 

10.  Birds 5  lessons 

11.  Fish  (and  frog,  if  this  form  is  taught)  ....  14  lessons 

12.  Single-celled  animals 5  lessons 

13.  The  general  structure  of  the  human  body     .     .  3  lessons 

14.  Microorganisms  and  their  relation  to  human  wel- 

fare        10  lessons 

15.  Nutrients  and  their  uses 7  lessons 

16.  Stimulants,  narcotics,  and  poisons 10  lessons 

17.  Digestion  of  the  nutrients 7  lessons 

18.  Circulation  of  the  nutrients 6  lessons 

19.  Respiration  and  the  production  of  heat  and 

power  in  man 7  lessons 

20.  Additional  topics  in  hygiene 9  lessons 


APPENDIX  III 

BIOLOGY  NOTE-BOOKS 

Method  of  Recording  Laboratory  Observations.  —  In  preparing 
note-book  records  of  laboratory  observations  or  experiments, 
home  work,  or  field  trips,  the  teacher  should  insist,  so  far  as  possible, 
that  pupils  give  in  clear,  concise  English  a  complete  account  of  the 
work  that  has  been  done.  Students  should  be  careful  to  state  the 
purpose  of  the  experiment,  and  describe  the  preparation  of  the  ex- 
periment. He  should  indicate  whether  the  work  was  done  by  him- 
self or  by  some  one  else.  The  results  observed  should  be  sharply 
distinguished  from  the  conclusions  derived  from  observation. 
Pupils  might  well  use  as  paragraph  titles  the  section  titles  printed 
in  heavy  face  type  (e.g.  Carbon,  Oxygen,  etc.).  On  pp.  182-183  are 
two  accounts  of  the  same  experiments  that  were  photographed  from 
the  note-books  of  two  different  pupils.  The  method  of  writing  up 
an  experiment  shown  in  Fig.  88  is  suggested  for  accounts  that  are 
written  in  the  laboratory ;  that  in  Fig.  89,  for  accounts  written  at 
home. 

Drawings.  —  In  making  drawings  pupils  should  be  supplied  with 
sharp-pointed  pencils  that  are  relatively  hard.  Clear  outline  draw- 
ings should  be  insisted  upon,  and  shading  should  as  a  rule  not  be 
encouraged  (Figs.  90,  91).  The  general  title  of  the  sheet  of  drawings 
should  be  placed  at  the  top  of  the  sheet.  When  there  are  several 
drawings  on  the  same  sheet,  the  general  title  should  be  placed  at  the 
top,  and  the  special  title  of  each  should  be  written  just  below  the 
individual  drawing.  In  labeling,  the  dotted  leaders  may  run  in  any 
direction  (see  pp.  184-187),  but  they  should  not  cross  each  other. 
The  labels,  however,  should  all  be  written  parallel  to  the  top  margin 

181 


182  APPENDIX  III 

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FIG.  88.  —  Specimen  page  from  a  note-book. 


APPENDIX  HI  183 


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FIG.  89.  —  Specimen  page  from  a  note-book. 


184 


APPENDIX  III 


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AshAcd/V 


OMjuoJ^/^OrO^.. 


(I 
FIG.  90.  —  Drawing  of  an  advanced  stage  of  the  corn  seedling. 


APPENDIX  III  185 

of  the  sheet.  If  the  drawings  are  made  on  separate  sheets  of  paper 
about  the  size  of  a  page  in  the  note-book,  the  sheets  may  be  col- 
lected, criticized,  and  rated,  and  then,  if  the  left-hand  margin  of  about 
an  inch  is  folded,  the  drawings  can  be  fastened  in  the  note-book  by 
pasting  this  narrow  flap. 

The  following  directions  for  guiding  pupils  in  the  preparation  of 
their  note-books  have  been  found  by  the  authors  to  be  of  great  assist- 
ance. 

1.  In  the  upper  right-hand  corner  of  the  outside  front  cover  of 

your  note-book  write  your  name,  division  (i.e.  grade  and 
section),  and  the  classroom  in  which  you  meet  at  9  A.M. 
thus: 

JOHN  S.  JONES,  1-8  (or  IA) 
Room  416 

Across  the  middle  of  the  front  cover  write  BIOLOGY  NOTE- 
BOOK. 

2.  Cover  your  note-book  with  manila  paper,  and  on  the  front 

cover  put  the  information  called  for  in  1  above.  Be 
sure  to  keep  your  note-book  covered. 

3.  Write  your  name,  division,  and  classroom  in  the  upper  right- 

hand  corner  of  the  first  page  of  your  note-book.  Leave 
the  rest  of  this  page  blank  for  the  teacher's  ratings  and 
comments. 

4.  Number  each  page  of  your  note-book. 

5.  On  each  of  the  pages  draw  a  vertical  line  about  an  inch  from 

the  left  margin.  Always  leave  this  marginal  space  for 
the  teacher's  comments. 

6.  Begin  each  new  subject  on  a  new  page,  writing  its  title  on  the 

first  line.  The  first  composition  or  notes  should  commence 
on  page  5,  the  preceding  pages  being  reserved  for  index. 

7.  Write  your  compositions  or  notes  in  ink  on  both  sides  of  the 

page. 

8.  Indent  about  an  inch  the  first  word  of  each  paragraph. 

All  other  lines  should  begin  at  the  left  margin  line.    It  is 


186  APPENDIX   III 

suggested  that  the  paragraph  titles  used  in  the  labora- 
tory studies  be  employed  and  that  they  be  underlined  (e.g. 
Parts  of  a  Leaf). 

9.  Make  sure  that  your  statements  in  each  paragraph  or  in 
your  notes  are  sufficiently  full  and  clear  to  be  readily 
intelligible  to  one  who  knows  nothing  of  the  subject. 

10.  In  your  compositions  or  notes  be  careful  to  make  clear  what 

you  yourself  did,  what  you  saw,  what  you  heard,  and  what 
you  read.  Accounts  of  experiments  may  often  be  written 
in  four  paragraphs  as  follows:  object  of  experiment; 
preparation  of  experiment;  result  of  experiment;  con- 
clusion from  experiment. 

11.  If,  on  account  of  absence,  it  is  necessary  that  work  be  copied, 

inclose  such  account  in  quotation  marks,  and  write  at 
the  end  of  such  quotation  the  name  of  the  pupil  from 
whom  the  account  was  copied. 

12.  Every  correction  indicated  by  the  teacher  should  be  made  by 

the  student  as  soon  as  the  note-book  is  returned. 

13.  Every  student  who  wishes  to  do  so  can  produce  a  first  class 

note-book,  neat  in  appearance,  and  at  least  relatively 
free  from  mistakes  in  spelling,  punctuation,  and  grammar. 

MARKS  USED  IN  THE  CORRECTION  OF  BIOLOGY  PAPERS 

cp  =  mistake  in  use  or  in  omission  of  capital  letter. 

cl   =  meaning  not  clear. 

gr  =  mistake  in  grammar. 

n   =  composition  is  lacking  in  neatness. 

IF   =  error  in  paragraphing. 

p    =  mistake  in  punctuation. 

r    =  repetition  of  word  or  idea. 

sp  =  error  in  spelling. 

w  =  word  improperly  used. 

?   =  doubt  as  to  the  truth  of  the  statement. 

( )  =  words  in  parenthesis  are  to  be  crossed  out. 

A  =  some  omission. 


APPENDIX  111 


18' 


FIG.  91.  —  Drawing  of  side  view  of  frog. 


APPENDIX  IV 

REVIEW  TOPICS  IN   PLANT  BIOLOGY 

You  should  be  prepared  to  give  a  good  oral  recitation  on  each  of  the 
following  topics.  If  you  are  not  sure  of  any  of  the  facts  called  for, 
write  down  the  topic  or  topics,  and  ask  your  teacher  at  the  beginning  of 
the  next  recitation  how  to  obtain  the  information. 

A.  COMPOSITION  OF  LIFELESS  AND  LIVING  THINGS. 

1.  Chemical  element:  definition ;  examples  with  symbols  of  each  ; 

characteristics  of  each  (i.e.  whether  it  is  solid,  liquid,  or  gas ; 
color,  odor,  and  taste ;  ability  of  each  to  burn  or  to  cause 
burning). 

2.  Oxidation:    definition;    chemical  element  necessary;    com- 

pound formed  by  the  oxidation  of  elements ;  evidences  of 
oxidation. 

3.  Chemical  compound:   definition;    examples;    test  for  two  of 

them,  with  characteristics  of  each  (as  in  1  above). 

4.  Food  substances :  kinds ;   chemical  composition  of  each ;  test 

for  each ;  examples  of  foods  containing  each  in  abundance. 

5.  Manufacture  of  food  substances  by  plants :  proofs  of  the  neces- 

sity of  sunlight,  chlorophyll,  and  carbon  dioxide  for  carbo- 
hydrate manufacture ;  proofs  of  the  excretion  of  oxygen  in 
carbohydrate  manufacture ;  manufacture  of  proteins. 

B.  GENERAL  STRUCTURE  OF  PLANTS. 

1.  Parts  of  a  plant ;  organs  and  functions. 

2.  Structure  of  plant  cells;  protoplasm;  assimilation,  growth, 

and  cell  division. 

188 


APPENDIX  IV  189 

C.  OSMOSIS  AND  DIGESTION. 

1.  Proofs  that  water  and  grape  sugar  will  pass  through  a  mem- 

brane ;  definition  and  law  of  osmosis. 

2.  Proofs  that  starch  and  protein  will  not  pass  through  a  mem- 

brane;  digestion  of  starch;   definition  of  digestion;   diges- 
tive ferments. 

D.  ADAPTATIONS  OF  THE  NUTRITIVE  ORGANS  OF  PLANTS. 

1.  Roots:  gross  structure;  structure  of  a  root-hair ;  functions  of 

roots ;  adaptations  of  roots. 

2.  Stems :  gross  structure  of  a  woody  stem ;  functions  of  stems ; 

adaptations  of  stems ;  changes  in  stems  during  growth. 

3.  Leaves:    gross   and   microscopical   structure;    functions   of 

leaves ;  adaptations  of  leaves. 

E.  RESPIRATION  AND  THE  PRODUCTION  OF  ENERGY  IN  PLANTS. 

1.  Energy:   examples  in  plants;    proof  that  heat  energy  is  de- 

veloped in  growing  seedlings ;    transformations  of  energy; 
source  of  energy ;  oxidation  as  a  means  of  liberating  energy. 

2.  Respiration:  definition;  proof  of  the  necessity  of  air  for  plants 

and  of  the  production  of  carbon  dioxide  by  plants. 

F.  REPRODUCTION  IN  SEED-PRODUCING  PLANTS. 

1.  Floral  envelopes:  names  of  the  parts  of  each  floral  envelope; 

position  and  general  description  of  the  floral  envelopes 
in  the  flowers  studied;  functions  of  each  of  the  floral 
envelopes. 

2.  Essential  organs:  name,  number,  position,  and  parts  of  each 

of  the  essential  organs;  general  description  and  func- 
tions of  the  parts  of  each  of  the  essential  organs. 

3.  Pollination. 

a.  Self-pollination :  definition ;  devices  to  prevent  it  in  flowers 

studied. 
6.  Cross-pollination :   definition ;   devices  to  make  it  possible 

in  flowers  studied ;  agencies  which  secure  cross-pollina- 


190  APPENDIX    IV 

tion;  comparative  vigor  of  plants  from  seeds  resulting 
from  cross-pollinated  and  from  self-pollinated  flowers. 

4.  Fertilization. 

a.  Cellular  nature  of  pollen  and  ovules ;  germination  of  pollen 

grains. 

b.  Structure  of  ovule. 

c.  Process  of  fertilization ;  production  of  the  embryo. 

5.  Fruits. 

a.  Structure  of  each  of  fruits  studied;  definition  of  a  fruit; 
classification  of  fruits. 

6.  Necessity  for  seed-dispersal ;  agencies  by  which  seed-dis- 
persal is  brought  about ;  adaptations  of  fruits  and  seeds 
to  secure  dispersal  by  each  of  these  agencies. 

c.  Adaptations  for  protecting  seeds  of  unripe  edible  fruits; 
adaptations  for  protecting  seeds  of  ripe  edible  fruits. 

G.  PLANT  PROPAGATION. 

1.  Bean  seed  and  its  development  into  a  seedling:   markings  on 

seed ;  their  cause  or  function ;  seed  covering ;  position 
and  kinds  of  stored  food;  description  of  parts  of  em- 
bryo; parts  of  the  plant  which  develop  from  the  parts 
of  the  embryo ;  breaking  of  seedling  through  the  soil. 

2.  (Optional.)     Corn  grain  and  its  development  into  a  seedling: 

description  of  the  parts  of  the  embryo;  position  and 
kinds  of  stored  food ;  breaking  of  seedling  through  the 
soil ;  various  parts  of  the  plant  which  develop  from  each 
of  the  parts  of  the  embryo. 

3.  Definitions:    seed,  seedling,  germination,  seed  coats,  micro- 

pyle,  hilum,  embryo,  cotyledon,  plumule,  hypocotyl, 
endosperm,  primary  and  secondary  roots. 

4.  Experiments  to  show  — 

a.  Function  of  endosperm  of  corn  grain. 
6.  (Optional.)     Relation  of  water  and  temperature  to  germi- 
nation. 

5.  (Optional.)     Other  methods  of  plant  propagation:  grafting; 

slips,  runners,  and  layers ;  tubers ;  bulbs. 


APPENDIX  IV  191 

6.  Conditions  essential  for  the  growth  of  plants :  five  essential  con- 

ditions ;  conditions  of  soil  favorable  for  growth ;  meth- 
ods of  soil  improvement. 

7.  (Optional.)     Struggle  for  existence  and  its  effects:    Variation 

among  plants ;  numbers  of  seeds  produced  by  plants ; 
struggle  for  existence  among  plants;  survival  of  the 
fittest. 

8.  (Optional.)     Improvement  of  plants  by  man:   artificial  selec- 

tion of  favorable  variations ;  artificial  crossing  of  related 
species ;  some  of  the  valuable  crops  of  New  York  State ; 
some  of  the  methods  of  increasing  crop  production. 

H.  PLANTS  IN  THEIR  RELATION  TO  HUMAN  WELFARE. 

1.  Some  uses  of  plants  to  man. 

a.  Uses  of  plants  for  food. 

b.  Uses  of  plants  for  flavoring  extracts,  beverages,  and  medi- 

cines. 

c.  Uses  of  plants  for  clothing. 

2.  Forests  and  forest  conservation.1 

a.  Definitions. 

•  (1)  A  forest  means  a  growth  of  trees  sufficiently  dense  to 
form  a  fairly  unbroken  canopy  of  trees.  A  forest 
has  a  population  of  animals  and  plants  peculiar 
to  itself,  a  soil  of  its  own  making,  and  a  climate 
different  from  that  of  the  open  country. 
(2)  "  Forestry  is  the  preservation  of  forests  by  wise  use."  — 
ROOSEVELT. 

b.  Value  of  forests. 

(1)  ^Esthetic  value  —  beauty  of  form  and  color  of  forest 

trees. 

(2)  Value  in  affecting  drainage. 

(a)  By  retaining  water  in  the  soil  through  the  agency 
of  the  roots. 

1  The  authors  are  indebted  to  Miss  Kate  B.  Hixon,  of  the  Morris 
High  School,  New  York,  N.Y.,  for  the  review  topics  on  Forests  and 
Forest  Conservation. 


192  APPENDIX    IV 

(6)  By  preventing  too  rapid  evaporation  from  the  soil, 

through  the  help  of  the  foliage. 
(c)  By  retarding  the  melting  of  snow,  thus  preventing 

freshets. 

(3)  Value  in  affecting  climate. 

(a)  By  bringing  moisture  into  the  air,  which  falls  as 

rain. 
(6)  By  setting  oxygen  free  into  the  air  in  the  process 

of  starch  making, 
(c)  By  acting  as  a  windbreak. 

(4)  Economic  value. 

(a)  As  a  source  of  lumber  and  fuel. 

(6)  As  a  source  of  food  (nuts,  maple  sugar,  etc.). 

(c)  As  a  source  of  industrial  raw  materials  (paper, 

tanning   materials,    wood    alcohol,    tar,    pitch, 

turpentine,  rosin,  fibers). 

c.  Dangers  to  forests. 

(1)  Fires.  (4)  Careless  lumbering. 

(2)  Insects.  (5)  Fungi  that  cause  disease. 

(3)  Grazing  of  cattle. 

d.  Results  of  deforestation. 

(1)  Main  cause  of  freshets,  which  cause  destruction  of 

property  and  loss  of  life ;  they  also  fill  up  navi- 
gable streams  with  soil  and  debris. 

(2)  Drouth,  with  the  consequent  lessening  of  water  power. 

(3)  Timber  famine,  especially  in  hard  woods. 

e.  Methods  used  by  the  Government  Bureau  of  Forestry  to 

preserve  forests. 

(1)  Allow  only  the  cutting  of  dead  or  mature  trees. 

(2)  Insist  that  each  tree  cut  be  replaced  by  another  of  the 

same  kind. 

(3)  Prevent  the  spread  of  fires. 

(4)  Destroy  insects  that  are  injurious  to  trees. 

(5)  Restrict  cattle  grazing  to  certain  seasons. 
3.  Fungi  and  their  relation  to  human  welfare. 

a.  Bacteria;   microscopical  appearance  and  size;   reproduc- 


APPENDIX  IV  193 

tion ;  necessary  conditions  for  growth ;  relation 
(1)  to  soil  fertility,  (2)  to  flavors  of  food,  (3)  to 
the  industries,  (4)  to  diseases. 

6.  (Optional.)  Yeast :  microscopical  appearance  and  size ; 
reproduction;  changes  caused  by  yeast;  uses 
of  yeast. 

c.  (Optional.)     Bread  mold;    structure;    reproduction  and 

life  history ;  nutrition  in  the  fungi. 

d.  (Optional.)     Other  fungi :  mushrooms,  rusts,  and  smuts ; 

economic  importance. 

I.  PLANT  CLASSIFICATION. 

1.  Common  methods  of  classification. 

a.  Herbs,  shrubs,  and  trees :  define  each ;  give  examples. 

b.  Annuals,   biennials,  and  perennials;    define  each;    give 

examples. 

c.  Deciduous  and  evergreen  trees  and  shrubs:   define  each; 

give  examples. 

2.  (Optional.)    Scientific  method  of  classification, 
a.  Seed-producing  plants. 

(1)  Gymnosperms  and  angiosperms. 

(2)  Monocotyledons  and  dicotyledons. 

(3)  Plant  family,  genus,  species,  variety. 
6.  Spore-producing  plants. 

(1)  Ferns:  fern  plant;  spores;    prothallus;  fertilization 

of  the  egg-cells ;  alternation  of  generations. 

(2)  Mosses :  moss  plant ;  protonema ;  sexual  generation ; 

alternation  of  generations. 

(3)  Algae :  Spirogyra,  its  structure,  methods  of  reproduc- 

tion   and    functions;    Pleurococcus  and  other 


(4)  Fungi  (see  H,  3,  above). 

Note.     The  following  outlines  were  prepared  by  Miss  Martha 
F.  Goddard,  late  of  the  Morris   High  School,  New  York,  N.Y. 
They  furnish  an  admirable  review  of  the  most  important  nutritive 
o 


194  APPENDIX    IV 

and  reproductive  functions  of  plants.  Pupils  might  either  copy 
the  whole  outline  into  their  note-books,  supplying  the  words  repre- 
sented by  the  figures,  or  make  a  list  of  the  words,  numbering  them 
to  correspond  to  the  figures  below. 

NUTRITION  IN  GREEN  PLANTS  THAT  PRODUCE   SEEDS 

Soil- water,  in  which  are  dissolved  compounds  that  contain  nitro- 
gen and  other  mineral  matters  needed  by  the  plant,  is  absorbed  by 
(1)  which  are  (2)  found  (3)  of  roots.  The  process  by  which  this  soil- 
water  enters  is  called  (4).  In  the  root-hair  the  membrane  is  the  (5). 
More  liquid  enters  the  root-hair  than  passes  out,  because  (6).  The 
substances  admitted  in  the  soil-water  are  regulated  by  the  action  of 
the  (7)  in  the  cell,  through  which  the  liquid  must  pass.  The  cell- 
sap  passes  from  one  cell  of  the  root  to  the  next,  until  it  reaches 
thick- walled  tubular  cells  called  (8),  which  form  part  of  the  (9)  of 
the  root,  stem,  and  leaf.  The  liquid  passes  up  through  these  un- 
til it  reaches  spaces  between  the  thin-walled  leaf-cells,  and  finally 
the  sap  gets  into  these  cells. 

A  gas  called  (10)  is  taken  in  through  epidermis  cells  of  the  leaf,  and 
through  openings  called  (11)  between  certain  cells  of  the  epidermis 
that  are  known  as  (12).  In  the  soft  cells  of  the  inside  of  the  leaf 
are  tiny  masses  of  protoplasm  which  contain  a  green  coloring  matter 
called  (13).  These  green  masses  of  protoplasm  are  called  (14). 
They  can  manufacture  starch  out  of  the  (15)  and  -the  (16)  in  the 
presence  of  (17).  VThe  elements  in  C02  and  H20,  however,  are  not 
in  quite  the  right  proportions,  so  (18)  is  given  off  as  a  waste  product. 
The  soil-water  is  such  a  weak  solution  of  mineral  matter  that  not  all 
the  water  can  be  used  by  the  plant,  so  this  water  that  is  not  needed 
is  given  off  by  a  process  called  (19).  The  amount  of  water  thus  given 
off  is  regulated  by  the  action  of  the  (20)  that  surround  each  (21). 

During  the  night  the  starch  is  changed  to  (22)  by  a  process  known 
as  (23).  This  liquid  food  then  passes  down  through  the  (24)  of 
the  veins  and  bast  or  fibrous  bark  to  places  that  serve  for  storage 
or  to  growing  regions  where  it  is  used  to  make  a  substance  for  cell- 
wall  building  known  as  (25).  Some  of  the  sugar  is  made  by  the  pro- 


APPENDIX  IV  195 

toplasm  of  the  plant  to  unite  with  the  nitrogen  of  the  nitrates  and 
with  the  sulphur  and  phosphorus  of  other  mineral  matters  derived 
from  the  soil,  and  a  compound  is  formed  called  (26)  which  the  grow- 
ing regions  use  to  make  into  more  (27).  This  last  change  is  called 
assimilation. 

Some  of  the  proteids  may  also  be  stored  for  future  use.  Food 
may  be  stored  in  the  (28),  the  (29),  the  (30),  the  (31),  or  in  any  thin- 
walled  cells. 

OPTIONAL.    THE  LIFE-HISTORY  OF  A  SEED-PLANT 

See  note,  p.  193. 

The  mother-plant  produces  flowers  which  attract  insects  by  their 
(1)  or  by  their  (2).  These  animals  carry  (3)  on  their  hairy  bodies 
from  the  (4)  of  one  flower  to  the  (5)  of  another.  Here  nourished 
by  a  (6)  it  sends  out  a  tube  which  grows  down  through  (a)  the  (7), 
(6)  the  (8),  and  (c)  the  (9),  and  here  enters  a  tiny  opening  called  the 
(10)  in  the  (11).  There  a  nucleus  of  the  pollen  grain  (called  a  sperm 
nucleus)  unites  with  a  nucleus  of  the  egg-cell  in  the  ovule  during  the 
process  of  (12)  to  form  one  cell  (called  a  fertilized  egg-cell)  which 
now  develops  into  a  tiny  plant  known  as  the  (13)  of  the  seed.  This 
little  plant  has  (a)  a  minute  stem  called  the  (14),  (b)  one,  two,  or 
more  seed-leaves  known  as  (15),  and  (c)  usually  a  tiny  bud  called  the 
(16). 

The  mother-plant  feeds  this  embryo  until  it  has  grown  thus  far, 
and  also  stores  up  food  for  further  growth.  This  may  be  put  in  the 
cotyledons  as  in  the  (17)  seed,  or  it  may  be  packed  around  the 
embryo,  when  it  is  called  (18),  as  in  the  (19).  To  protect  the  embryo 
until  time  for  germination,  the  seed  has  one  or  more  outer  coverings 
known  as  (20).  That  the  seed  may  be  carried  away  from  the  mother- 
plant,  and  so  have  better  opportunities  for  development,  the 
mother-plant  provides  the  fruit  or  the  seeds  (a)  with  (21)  or  (22)  so 
they  may  be  carried  by  the  wind,  or  (b)  with  (23)  so  they  may  cling  to 
the  wool  of  animals,  or  (c)  with  (24)  so  they  may  tempt  animals  to 
eat  them ;  in  the  last  case  (as  in  the  peach  or  cherry)  the  contents 
of  the  seed  are  protected  by  (25). 


196  APPENDIX    IV 

When  the  seed  has  favorable  surroundings,  namely  (26),  (27), 
and  (28),  it  germinates.  If  it  has  one  cotyledon,  the  plant  is 
called  (29),  the  woody  bundles  in  its  stem  will  be  (30),  and  the 
veining  of  the  leaves  will  probably  be  (31).  If  two  cotyledons  are 
present  in  the  seed,  the  plant  is  called  (32),  the  woody  bundles  in 
its  stem  will  be  arranged  (33),  and  the  veining  of  the  leaves  will 
be  (34). 

The  principal  food  materials  stored  in  seeds  are  three  in  number, 
namely,  (a)  (35),  which  is  tested  by  (36) ;  (6)  (37),  tested  by  (38) ; 
and  (c)  (39),  tested  by  (40).  Sometimes  a  fourth  nutrient  (41)  is 
stored  in  other  parts  of  the  plant ;  its  presence  may  be  detected 
by  (42). 


APPENDIX  V 

REVIEW  TOPICS  IN  ANIMAL  BIOLOGY 

The  student  should  be  prepared  to  give  a  good  oral  recitation 
on  each  of  the  following  topics.  If  he  is  not  sure  of  any  of  the  facts 
called  for,  he  should  write  down  the  topic  or  topics,  and  ask  the 
teacher  at  the  beginning  of  the  next  recitation  how  to  obtain  the 
information. 

A.  INSECTS. 

1.  Butterflies  and  moths. 

a.  Characteristics  of  structure :  regions ;  organs  of  the  head 
(eyes,  antennae,  proboscis) ;  wings  and  their  scales ; 
legs;  abdomen. 

6.  (Optional.)  Experiments  to  show  methods  of  feeding  and 
flying. 

c.  Reproduction  and  life  history. 

d.  Economic  importance :  cabbage  butterfly ;  tussock  moth ; 

gypsy  moth ;  brown-tail  moth ;   codling  moth ;   clothes 
moth;  silkworm. 

2.  Grasshoppers  and  their  relatives. 

a.  Characteristics  of  structure :  regions ;  organs  of  the  head 
(eyes,  antennas,  mouth  parts);  legs  and  their  parts; 
wings;  abdomen. 

6.  Experiments  to  show  methods  of  feeding,  locomotion,  and 
breathing. 

c.  Reproduction  and  life  history;  direct  and  indirect  meta- 

morphosis. 

d.  Economic  importance ;  relatives  of  the  grasshopper. 

3.  Bees  and  their  relatives. 

a.  Characteristics  of   structure;    regions;    organs  of  head 
197 


198  APPENDIX    V 

(eyes,  antennae,  mouth  parts) ;    adaptations  of  mouth 
parts  and  legs  for  collecting  nectar  and  pollen. 
6.  Queen  arid  drones :  reproductive  functions  of  each. 

c.  Work  of  the  hive:    comb  building;    pollen  gathering; 

honey  making ;   care  of  young ;  protection  and  ventila- 
tion of  the  hive. 

d.  History  of  beekeeping;  life  history  of  honeybee;  swarming. 

e.  Economic  importance  of  bees. 
/.   Relatives  of  bees. 

4.  Mosquitoes  and  flies. 

a.  Life  history  of  house  mosquito  (Culex). 

b.  Life  history  of  malaria-transmitting  mosquito  (Anopheles). 

c.  Proofs  that  malaria  is  transmitted  by  Anopheles  mosquito ; 

life  history  of  malaria  parasite. 

d.  Proofs  that  yellow  fever  is  transmitted  by  Stegomyia 

mosquito. 

e.  Methods  of  exterminating  mosquitoes. 

/.  House  flies:    feeding  habits;    relation  to  disease;    life 
history ;  methods  of  extermination. 

5.  (Optional.)     Other  topics  on  insects, 
a.  Losses  due  to  insect  pests. 

6*  Insecticides. 
B.  BIRDS. 

1.  Characteristics  of  structure:  regions;   organs  of  head;  wings 

and  their  adaptations  for  flight ;   (optional)  legs. 

2.  Reproduction  and  life  history:    structure  and  formation  of 

egg;  fertilization  and  development  of  embryo;  nests 
and  care  of  young. 

3.  (Optional.)     Classification  of  birds :  common  methods  of  clas- 

sification; scientific  classification  with  characteristics  of 
each  group  (e.g.  swimming,  wading,  and  scratching  birds ; 
birds  of  prey;  woodpeckers;  perching  birds). 

4.  (Optional.)     Migration  of  birds :  identification  of  birds. 

5.  Importance  of  birds  to  man:   as  destroyers  of  harmful  in- 

sects; as  destroyers  of  weed  seeds;  as  destroyers  of  rats 
and  mice ;  as  scavengers. 


APPENDIX    V  199 

6.  Birds  injurious  to  man. 

7.  Decrease  in  bird  life:    by  cats;    by  boys;    for  food;    for 

millinery  purposes ;   effects  of  bird  destruction. 

8.  Conservation  of  birds :   legislation ;   creatioit  of  public  senti- 

ment ;  how  girls  and  boys  can  help ;  feeding  of  birds  and 
building  of  bird  houses. 

C.  FROGS  AND  THEIR  RELATIVES. 

1.  Characteristics  of  structure:    regions;    organs  of  head  with 

position  of  each;  arms  and  legs,  position  and  parts  of 
each. 

2.  Locomotion:  adaptation  for  swimming  and  jumping. 

3.  Food  getting  and  digestion :  kinds  of  food  eaten ;  adaptations 

for  securing  and  swallowing  food;  digestive  organs  and 
digestion. 

4.  Circulation:  parts  of  circulatory  system  with  adaptations  of 

each. 

5.  Breathing  and  respiration:   definitions;   location  of  air  pas- 

sages and  lungs ;  inspiration  and  expiration ;  adaptations 
of  lungs,  blood  vessels,  and  skin ;  oxidation  and  the  release  of 
energy. 

6.  Habits  of  frogs :  enemies;  adaptations  for  protection. 

7.  Reproduction:   formation  of  eggs;   development  of  embryo.; 

changes  in  organs  of  locomotion,  digestion,  circulation, 
and  respiration  during  life  history. 

8.  Relatives  of  frogs. 

9.  Economic  importance  of  Amphibia. 

D.  FISHES. 

1.  Characteristics  of  structure:    regions;    organs  of  head  with 

position  of  each ;  structure  of  fins ;  differences  in  form  of 
body  and  position  of  fins  in  various  kinds  of  fishes. 

2.  Locomotion:  adaptations  of  body  regions  and  fins. 

3.  Food  getting  and  digestion :  kinds  of  food  eaten ;   adaptation 

for  securing  and  swallowing  food;  digestive  organs  and 
digestion. 

4.  Circulation:    parts  of  circulatory  system  with  adaptations 

of  each. 


200  APPENDIX    V 

5.  Breathing  and  respiration :  definitions ;  breathing  movements, 

cause  and  effect  of  each;   adaptations  of  gills  (including 
blood  vessels) ;  oxidation  and  the  release  of  energy. 

6.  Reproduction :  formation  of  eggs  and  sperm-cells ;  fertilization ; 

development  of  embryo ;  food  supply  for  embryo ;  artificial 
propagation. 

7.  Economic  importance :    (a)  for  food,  (b)  for  other  purposes ; 

methods  of  preparing  fish. 

8.  Salmon  and  codfish:    geographical  distribution;    food  and 

feeding  habits ;  breeding  habits ;  methods  of  catching. 

9.  Conservation  of  fish :  disappearance  of  Atlantic  salmon ;   de- 

crease of  Pacific  salmon;    work  of  National  and  State 
Governments ;  laws  for  the  protection  of  fishes. 

E.  CRAYFISHES  AND  THEIR  RELATIVES. 

1.  Regions  and  appendages. 

2.  Adaptations  for  walking  and  swimming. 

3.  Food,  food  getting,  and  digestion. 

4.  Adaptations  for  breathing ;  respiration  and  the  production  of 

energy. 

5.  Habits:  enemies;  adaptations  for  protection. 

6.  Reproduction  and  life  history. 

7.  Relatives  of  crayfish. 

8.  Economic  importance  of  Crustacea. 

F.  PROTOZOA. 

1.  Paramecium:  structure;  locomotion;  food,  food  getting  and 

digestion;  respiration  and  liberation  of  energy;  excretion; 
reproduction. 

2.  (Optional.)     Amoeba:   (use  same  topics  as  in  1  above). 

3.  Comparison  of  Protozoa  with  higher  animals. 

4.  Economic  importance  of  Protozoa. 

G.  (Optional.)    ADDITIONAL  ANIMAL  STUDIES. 

1.  Sponges:  structure;  functions;  economic  importance. 

2.  Hydra :  structure ;  adaptations  for  locomotion,  food  getting, 

digestion,  and  respiration ;  reproduction ;  relatives. 

3.  Earthworm:   structure;  adaptations   for   locomotion;    food 

getting  and  digestion;  economic  importance ;  relatives. 


APPENDIX    V  201 

4.  Fresh-water  mussel:    structure;   adaptations  for  protection, 

locomotion,  eating,  and  breathing;   relatives. 

5.  Turtle:    structure;    adaptations  for  protection,  locomotion, 

and  eating ;  relatives. 

6.  Mammals :  distinguishing  characteristics  of  structure ;  sense 

organs ;  teeth ;  appendages ;  economic  importance ;  repro- 
duction. 


APPENDIX   VI 

REVIEW  TOPICS  IN  HUMAN  BIOLOGY 

The  student  should  be  prepared  to  give  a  good  oral  recitation  on 
each  of  the  following  topics.  If  he  is  not  sure  of  any  of  the  facts 
called  for,  he  should  write  down  the  topic  or  topics  and  ask  the 
teacher  at  the  beginning  of  the  next  recitation  how  to  obtain  the 
information. 

A.  THE  GENERAL  STRUCTURE  OF  THE  HUMAN  BODY. 

1.  Regions  of  the  human  body:    external  regions;    general  plan 

of  internal  structure. 

2.  Organs  of  the  body :   definition ;   examples,  with  functions  of 

each.  ^<^i  ,YV<^ ,  u 

3.  Tissues  of  the  body:  examples,  with  characteristics  of  each. 

4.  Cells  of  the  body :  protoplasm;  assimilation,  growth,  and  cell 

division;  cells  of  mouth;  cells  of  the  blood,  and  of  other 
tissues. 

B.  MICROORGANISMS  AND  THEIR  RELATION  TO  HUMAN  WELFARE. 

1.  Bacteria:   microscopical  appearance  and  size;   reproduction; 

spore  formation. 

2.  Occurrence  of  bacteria:   proofs  of  their  presence,  (a)  in  air, 

(b)  in  water,  milk,  and  other  floods,  (c)  on  various  parts  of 
the  human  body ;  effects  of  (a)  different  degrees  of  tem- 
perature (including  Pasteurization  of  milk),  (6)  lack  of 
moisture,  (c)  antiseptics. 

3.  Bacteria  as  the  friends  of  man:    relation,  (a)  to  soil  fertility, 

(b)  to  flavors  of  food,  (c)  to  linen  and  other  industries. 

4.  Bacteria  as  the  foes  of  man:    injurious  effects  of  bacteria; 

methods  of  food  preservation ;  proper  methods  of  sweeping 
and  dusting,  with  experiments ;  treatment  of  cuts ;  tuber- 
202 


APPENDIX   VI  203 

culosis,  its  cause,  prevention,  and  cure;  pneumonia, 
cause  and  prevention;  diphtheria,  its  cause,  treatment, 
and  prevention ;  typhoid  fever,  its  cause  and  prevention ; 
water  and  milk  supplies;  (optional)  smallpox  and  vac- 
cination; (optional)  hydrophobia  and  the  Pasteur  treat- 
ment ;  cause  and  prevention  of  other  diseases ;  safeguards 
of  the  body  against  disease. 

C.  FOODS  AND  THEIR  USES. 

1.  Food  substances  found  in  the  human  body:  presence  of  pro- 

teins, fats,  carbohydrates,  mineral  matters,  and  water 
in  various  parts  of  the  human  body. 

2.  Necessity  of  foods:  (a)  for  growth,  (6)  for  repair,  (c)  for  the 

production  of  energy. 

3.  Definition  of  a  food. 

4.  Composition  of  foods :    food  substances  in  milk ;    difference. 

in  the  composition  of  animal  and  vegetable  foods. 

5.  Uses  of  each  of  the  food  substances:  comparison  of  the  uses  of 

the  nutrients. 

6.  Cooking  of  foods :  importance  of  proper  cooking ;  reasons  for 

cooking  animal  foods;  principles  involved  in,  (a)  frying, 
(6)  making  soups,  (c)  stewing,  (d)  boiling  meats,  (e)  roasting 
and  broiling;  reasons  for  cooking  vegetables;  boiling 
vegetables ;  bread  making. 

7.  Food  economy:   importance  of  food  economy;    comparative 

cost  of  foods ;  economy  in  the  purchase  of  foods ;  economy 
in  the  use  of  foods. 

8.  Daily  diet :  amount  of  each  nutrient  required ;  necessity  for 

a  mixed  diet ;  avoidance  of  indigestible  foods ;  sugar  as  a 
part  of  the  diet. 

D.  STIMULANTS  AND  NARCOTICS. 

1.  Definition  and  examples  of  each. 

2.  Tea  and  coffee :  preparation  of  each ;  effect  of  each  on  body ; 

use  and  abuse  of  each. 

3.  Chocolate,  cocoa,  and  other  beverages:    composition;    effects 
•      on  body. 

4.  Alcoholic  beverages :  composition ;  alcohol  as  a  stimulant  and 


204  APPENDIX   VI 

narcotic ;  effects  of  small  and  large  quantities  of  alcohol ; 
Professor  Hodge's  experiment  on  dogs,  as  to  the  effects 
of  moderate  amount  of  alcohol  in  relation  to,  (a)  activity, 
(6)  skill  and  endurance,  (c)  nervousness,  (d)  offspring  of  the 
dogs,  (e)  resistance  to  disease ;  effect  of  alcohol  on  human 
beings  in  relation  to,  (a)  mental  activity,  (6)  muscular 
activity,  (c)  manual  dexterity,  (d)  resistance  to  disease; 
alcohol  and  life  insurance;  business  arguments  for  total 
abstinence ;  cost  of  intemperance. 

5.  Tobacco:  effects,  (a)  on  growth,  (6)  on  mental  development; 

tobacco  and  athletics. 

6.  Drugs  and  patent  medicines:    opium  (morphine,  laudanum, 

paregoric) ;  acetanilid ;  dangers  in  the  use  of  patent  medi- 
cines ;  pure  food  and  drug  law. 
E.  DIGESTION  AND  ABSORPTION. 

1.  General  survey  of  the  digestive  system:  necessity  for  digestion ; 

parts  of  the  alimentary  canal ;  digestive  glands. 

2.  Mouth  cavity:    walls  of  the  mouth  cavity;    structure  and 

functions  of  the  tongue. 

3.  Teeth :  arrangement,  kinds,  number  of  each  kind,  functions ; 

milk  teeth ;  structure  and  care  of  teeth. 

4.  Saliva  and  its  functions :  experimental  proof  of  the  digestion 

of  starch  by  saliva ;  position  and  action  of  salivary  glands ; 
uses  of  saliva. 

5.  (Optional.)     Throat  cavity  and  gullet :  structure;  functions. 

6.  Stomach:  position,  size,  shape ;  lining  of  stomach  and  gastric 

glands ;  muscles  of  stomach ;   digestion  in  the  stomach. 

7.  Small  intestine :  position,  form,  size ;  (optional)  peritoneum ; 

digestion  in  the  small  intestine. 

8.  (Optional.)     Large  intestine:  position,  form,  size;  vermi- 

form appendix. 

9.  Absorption  from  the  alimentary  canal:  necessity  for  absorp- 

tion ;   absorption  in  mouth,  throat,  gullet,  and  stomach ; 
absorption  in  the  small  and  large  intestine. 
10.  (Optional.)     Liver:  position,  form,  size;  functions  of  the 
liver ;  functions  of  the  bile. 


APPENDIX   VI  205 

11.  Hygiene  of  digestion:  hygienic  habits  of  eating;  prevention 
of  disease ;  the  use  of  water  as  a  drink ;  effect  of  alcoholic 
drinks  on  the  organs  of  digestion. 

F.  CIRCULATION  OF  THE  NUTRIENTS. 

1.  Blood:    structure   of   corpuscles;    composition  of  plasma; 

hygiene  of  plasma. 

2.  Circulation :  definition ;  necessity  for ;  organs  of  circulation, 

definition  of  each. 

3.  Heart:  position,  size,  shape;  chambers,  position  and  struc- 

ture of  each ;  valves ;  action  of  heart. 

4.  Blood  vessels:  position  and  structure  of  arteries;   variations 

in  pulse  rate ;  valves  in  arteries ;  position,  importance,  and 
structure  of  capillaries :  position  and  structure  of  veins. 

5.  Course  of  the  blood  through  the  body :  changes  in  the  composi- 

tion .of  the  blood. 

6.  Hygiene  of  the  circulation:  effect  of  exercise  on  the  heart  and 

blood  vessels ;  stopping  of  blood  flow  in  wounds. 

G.  RESPIRATION  AND  THE  PRODUCTION  OF  ENERGY  IN  MAN. 

1.  Necessity  for  respiration:   proofs  of  oxidation  in  the  human 

body ;  examples  of  energy  in  the  human  body ;  transfor- 
mations of  energy ;  respiration  in  plants,  in  animals,  and  in 
man. 

2.  Adaptations  for  securing  oxygen  and  for  excreting  carbon  dioxid: 

course  taken  by  the  air ;  nose  cavity ;  throat  and  larynx ; 
lining  of  the  air  passages;  the  lungs,  their  structure  and 
blood  supply ;  function  of  red  corpuscles ;  change  in  color 
of  blood  after  mixing  with  oxygen ;  hygiene  of  red  corpus- 
cles. 

3.  The  process  of  breathing:    structure   of  the   chest   cavity; 

(optional)  pleura;  enlargement  of  chest  cavity;  how  air 
is  taken  into  the  lungs;  breathing  capacity  of  lungs; 
expiration. 

4.  Hygiene  of  respiratory  organs:   hygienic  habits  of  breathing; 

effect  of  exercise  on  respiration;  effect  of  tight  clothing 
upon  respiration;  diseases  of  respiratory  organs;  suffo- 
cation; necessity  of  ventilation;  methods  of  ventilation. 


206  APPENDIX   VI 

H.  (Optional.)    ADDITIONAL  TOPICS  IN  HUMAN  BIOLOGY. 

1.  The  skin:    characteristics;    uses;    layers;    glands;    impor- 

tance of  bathing ;  kinds  of  baths ;  care  of  the  hair ;  care 
of  the  nails ;  treatment  of  burns ;  clothing ;  effect  of  alcohol 
on  body  temperature. 

2.  The  skeleton :  necessity  for  the  skeleton ;  skeleton  of  the  neck 

and  trunk ;  skeleton  of  the  arms  and  legs ;  skeleton  of  the 
head ;  joints ;  food  and  the  skeleton ;  effect  of  pressure  on 
the  bones ;  fractures ;  dislocations ;  sprains. 

3.  The  muscles :  importance  of  muscle  tissue ;   kinds  of  muscle ; 

conditions  necessary  for  healthy  muscles  (food,  fresh  air, 
exercise,  rest) ;  relation  of  muscles  to  posture. 

4.  The  nervous  system:    the  body  as  a  collection  of  organs; 

cooperation  of  the  organs;  functions  of  the  nervous  sys- 
tem; parts  of  the  nervous  system;  cellular  structure  of 
the  nervous  system;  nerve  impulses;  reflex,  conscious, 
and  habitual  activities;  importance  of  habit;  conditions 
necessary  for  a  healthy  nervous  system  (food,  fresh  air, 
varied  activity,  rest) ;  effect  of  alcohol  on  the  nervous 
system. 

5.  The  eyes:    protection  for  the  eyes;    structure  of  the  eye; 

the  eye  as  a  camera ;  sensations  of  sight ;  defective  eyes ; 
hygiene  of  the  eyes. 

6.  The  ears:   the  external  ear;   the  middle  ear;   sensations  of 

sound. 
I.    (Optional.)    THE  LIVES  AND  WORKS  OF  GREAT  BIOLOGISTS. 


APPENDIX  YII 

LIST  OF  SUGGESTED  BOOKS  OF  REFERENCE  IN  BIOLOGY 
GENERAL   BIOLOGY 

1.  Cyclopedia  of  American  Agriculture.     Edited  by  L.  H.  Bailey. 

4  vols.— The  Macmillan  Co.,  N.  Y.  City.  $20  net. 
Vol.  I,  Farms;  Vol.  II,  Crops;  Vol.  Ill,  Animals;  Vol.  IV, 
The  Farm  and  the  Community.  We  do  not  hesitate  to  say 
that  Vols.  II  and  III  of  this  series  are  the  most  valuable 
books  of  reference  known  to  us  for  teachers  or  students  in 
plant  and  animal  biology.  Experts  on  the  many  subjects 
treated  have  epitomized  in  a  readable  form  a  vast  amount  of 
information  which  could  only  be  found  by  patient  search 
through  many  volumes.  If  schools  cannot  purchase  these 
books,  teachers  might  well  urge  that  they  be  put  on  the 
shelves  of  the  public  library,  for  all  four  volumes  will  be 
found  of  great  value  as  books  of  general  reference,  especially 
in  rural  communities. 

2.  Nature  Study  and  Life,  by  Dr.  C.  F.  Hodge.— Ginn  and  Co. 

$1.20.  Contains  many  suggestions  for  the  teaching  of  both 
plant  and  animal  biology. 

3.  General  Biology,  by  Sedgwick  and  Wilson. — Henry  Holt  and 

Co.  $1.75.  While  mainly  devoted  to  a  consideration  of 
the  earthworm  and  the  fern  (both  optional  topics),  this 
book  will  give  teachers  a  clear  idea  of  the  biology  of  a  plant 
and  of  an  annual,  and  of  the  composition  and  character- 
istics of  protoplasm.  It  also  contains  an  admirable  account 
of  yeast,  bacteria,  Amoeba,  and  Paramecium. 

4.  Teaching    of    Biology,    by  Lloyd  and  Bigelow.  —  Longmans, 

Green  and  Co.    $1.50.    Deals  largely  with  methods  of  teach- 
ing nature  study,  botany,  zoology,  and  human  physiology. 
207 


208  APPENDIX   VII 

PLANT  BIOLOGY 

5.  Practical  Botany,  by  Bergen  and  Caldwell. — Ginn  and  Co. 

$1.30. 

6.  College  Botany,  by  G.  F.  Atkinson.  —  Henry  Holt  and  Co. 

$1.50. 

7.  Readers   in   Botany,   by  Jane   C.   Newell. — Ginn  and   Co. 

2  vols.     $.60  each. 

8.  How  to  know  the  Wild  Flowers,  by  Mrs.  William  Starr  Dana. 

—The  Macmillan  Co.     $1 .50. 

9.  How  to  know  the  Fruits,   by  Maude  G.    Peterson.  —  The 

Macmillan  Co.     $1.50. 

10.  Tree  Book,  by  Julia  E.  Rogers. — Doubleday,  Page  and  Co.  $4. 

11.  Primer  of  Forestry.    Vols.   I    and   II.     Gifford   Pinchot.— 

U.  S.  Dept.  of  Agriculture. 

12.  New  Creations  in  Plant  Life,  by  W.  S.  Harwood.— The  Mac- 

millan Co.    $1.75. 

13.  Bacteria,  Yeast,  and  Moulds  in  the  Home,  by  H.  W.  Conn. — 

Ginn  and  Co.     $1. 

14.  Farmers'  Bulletins,  which  can  be  obtained  free  by  applying  to 

the  U.  S.  Dept.  of  Agriculture,  Washington,  D.C.  The 
various  Bulletins  contain  many  important  facts  relating 
to  both  animals  and  plants. 

ANIMAL  BIOLOGY 

15.  Animal  Life,  by  Jordan  and  Kellogg. — Appleton.    $1.20. 

16.  General  Zoology,  by  Linville  and  Kelly. — Ginn  and  Co.     $1.50. 

17.  American    Natural    History    (vertebrates   only),   by  W.   T. 

Hornaday.     $3.50. 

18.  Our  Vanishing  Wild  Life,  by  W.  T.  Hornaday.— Chas.  Scribner's 

Sons.    $1.50. 

19.  Insect  Book,  by  L.  0.  Howard.  —  Doubleday,  Page  and  Co.   $3. 

20.  Manual  of  Insects,  by  Comstock. — Comstock  Publishing  Co., 

Ithaca,  N.Y.     $3.75. 

21.  Insect  Pests  of  Farm,  Garden,  and  Orchard,  by  E.  D.  Sander- 

son.—John  Wiley.    $3. 


APPENDIX  VII  209 

22.  Birds  of  Northeastern  United  States,  by  Frank  Chapman. — 

Appleton.     $3. 

23.  Bird  Life  (with  colored  plates),  by  Frank  Chapman. — Apple- 

ton.    $2. 

24.  Relation  of  Birds  to  Man,  by  Weed  and  Dearborn.    Lippincott. 

$2.50. 

25.  Useful  Birds  and  their  Protection.    Forbush.    Mass.  Dept.  of 

Agriculture,  Boston,  Mass.    $1. 

26.  Food  and  Game  Fishes,  by  Jordan  and  Evennan.  — Doubleday, 

Page  and  Co.  $4. 

27.  Farmers'  Bulletins  (see  14  above). 

28.  Story  of  the  Fishes,  by  J.  N.  Basket!.— Appleton.     $.65. 

HUMAN  BIOLOGY 

29.  The  Human  Mechanism,  by  Hough  and  Sedgwick. — Ginn  and 

Co.    $2.50. 

30.  General   Physiology,  by  W.   H.   Howell  —  W.  B.   Saunders. 

$4. 

31.  Studies  in   Physiology,  by  James  E.  Peabody.  —  The  Mac- 

millan  Co.     $1.10. 

32.  Laboratory  Exercises  in  Anatomy  and  Physiology,  by  James 

E.  Peabody.—  Henry  Holt  and  Co.    $.60. 

33.  Infection   and   Immunity,   by  George  M.   Sternberg. —  Put- 

nams.     $1.75. 

34.  Pathogenic  Microorganisms,  by  W.  H.  Park. — Lea  Brothers 

and  Co.    $3.75. 

35.  Walter  Reed  and  Yellow  Fever,  by  H.  A.  Kelly.— McClure, 

Phillips  and  Co.    $1.50. 

36.  The    Malaria    Mosquito,    by    B.    E.    Dahlgren. — American 

Museum  of  Natural  History.     $.15. 

37.  Fresh  Air  and  How  to  Use  It.     Dr.  Thomas  Specs  Carrington. 

—  National  Association  for   the   Study  and   Prevention  of 
Tuberculosis,  103  E.  22d  St.,  New  York.    $1. 

38.  Physiological  Aspects  of  the  Liquor  Problem  (2  vols.).     Dr. 

John  S.  Billings  et  al.     Houghton  &  Mifflin.    $4.50. 


INDEX 


A.  B.  =  Animal  Biology;   H. B.  =  Human  Biology;   P.  B.  =  Plant  Biology. 


Abdomen,  A.  B.,  6,  151. 
Abdominal  cavity,  H.  B.,  1,  Fig.  1. 
Absorption, 

in  fish,  A.  B.,  131. 

in  frog,  A.  B.,  110. 

in  man,  H.  B.,  98-101. 
Accommodation  of  eye,  H.  B.,  163. 
Acetanilid,  H.  B.,  78,  Fig.  24. 
Adenoids,  H.  B.,  134. 
Aerial  roots,  P.  B.,  102. 
Agar,  nutrient,  for  growth  of  bacteria, 

H.  B.,  14. 

Ailanthus  fruit,  P.  B.,  92. 
Air, 

need  of,  for  growth,  P.  B.,  67. 

relation  of,  to  soil,  P.  B.,  111. 
Air  roots,  P.  B.,  102. 
Air  sacs,  H.  B.,  125,  127,  Fig.  41. 
Air  spaces,  P.  B.,  60,  62,  Fig.  22. 
Alcohol, 

as  a  possible  food,  H.  B.,  67. 

as  a  stimulant  and  narcotic,  H.  B., 
67. 

effect  of  moderate  amount  on  dogs, 
H.  B.,  68-72. 

effect  on  manual  dexterity,  H.  B., 
72. 

effect  on  mental  activity,  H.  B.,  72. 

effect  on  muscular  activity,  H.  B., 
72. 

effects  of  small  and  large  quantities 
H.  B.,  68. 

formed  by  yeast,  P.  B.,  147. 

relation     to     body     temperature, 
H.  B.,  143. 

relation  to  digestion,  H.  B.,  104. 

relation  to  disease,  H.  B.,  73. 

relation  to  life  insurance,  H.  B.,  73. 

relation  to  nervous  system,  H.  B., 
161. 


Alcoholic  beverages,  H.  B.,  66-75. 
Algse,  P.  B.,  166-169. 
Alimentary  canal, 

of  fish,  A.  B.,  130,  Fig.  98. 

of  frog,  A.  B.,  110,  Fig.  80. 

of  man,  H.  B.,  82,  Fig.  26. 
Alternate  arrangement,  P.  B.,  52. 
Alternation  of  generations, 

in  fern,  P.  B.,  163. 

in  moss,  P.  B.,  166. 
Amceba,  A.  B.,  170-171. 
Anaemia,  H.  B.,  129. 
Angiosperms,  P.  B.,  159,  170. 
Animal  foods,  composition  of,  H.  B., 

Fig.  19. 

Annelida,  A.  B.,  179. 
Annual,  an,  P.  B.,  156. 
Annual  rings,  P.  B.,  47,  51,  Fig.  17. 
Annual  scars,  P.  B.,  55. 
Anopheles  mosquito,  A.  B.,  46,  174, 

Fig.  32;  H.  B.,  42. 
Antenna, 

of  bee,  A.  B.,  31. 

of  butterfly,  A.  B.,  6. 

of  crayfish,  A.  B.,  151. 

of  grasshopper,  A.  B.,  22. 
Anterior,  A.  B.,  6. 

Anther,  P.  B.,  71,  73,  81,  88,  Fig.  25. 
Antheridia, 

of  fern,  P.  B.,  162,  Fig.  83,  D. 

of  moss,  P.  B.,  164. 
Antiseptics,     effect     on     growth     of 

bacteria,  H.  B.,  20. 
Antitoxins,  H.  B.,  35. 
Anti-typhoid  vaccine,  H.  B.,  37. 
Ants,  A.  B.,  43. 
Aorta,  H.  B.,  117. 
Apparatus,  price  list  of,  P.  B.,  173- 

175. 
Appendages,  A.  B.,  6. 


211 


212 


INDEX 


Appendicitis,  H.  B.,  98. 
Apple, 

fruit,  P.  B.,  Figs.  37,  38. 

leaves,  P.  B.,  Fig.  19. 
Archegonia, 

of  fern,  P.  B.,   163,  Fig.  83,  F. 

of  moss,  P.  B.,  164,  Fig.  84. 
Arm,    skeleton   of,    A.    B.,    Fig.   48; 

H.  B.,  146,  Fig.  44. 
Army  sanitation,  H.  B.,  38. 
Arsenate  of  lead,  A.  B.,  19,  61. 
Arteries, 

of  fish,  A.  B.,  131. 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  109,  112,  Fig.  35. 
Artificial  crossing  of  related  species, 

P.  B.,  120. 
Artificial  propagation  of  fish,  A.  B., 

140,  Fig.  105. 

Artificial  respiration,  H.  B.,  136. 
Artificial  selection,  P.  B.,  119. 
Asexual  generation, 

of  fern,  P.  B.,  163. 

of  moss,  P.  B.,  166. 
Asparagus,  P.  B.,  127. 
Assimilation,  P.  B.,  31;  H.  B.,  6. 
Astigmatism,  H.  B.,  164. 
Athletics  and  tobacco,  H.  B.,  77. 
Auricle, 

of  fish,  A.  B.,  132,  Fig.  100. 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  110,  Fig.  33. 

Bacillus  form  of  bacteria,  P.  B.,  Fig. 

71,  B,  C,  D;    H.  B.,  Fig.  7. 
Bacillus  tuberculosis,  H.  B.,  31,  Fig. 

14. 

Bacteria,    P.    B.,    140-145;     H.  B., 
10-43. 

as  foes  of  man,  H.  B.,  23-43. 

as  friends  of  man,  H.  B.,  20-22. 

definition,  H.  B.,  11,  Fig.  7. 

occurrence,  H.  B.,  14-20. 
Bamboo,  P.  B.,  49,  Fig.  18. 
Barbs  of  feather,  A.  B.,  68,  Fig.  50. 
Bark,  P.  B.,  45. 
Bast,  P.  B.,  46. 
Bathing,  H.  B.,  141. 
Bean  fruit,  P.  B.,  89. 


Bean  seed,  P.  B.,  97-100. 
Bedbug,  A.  B.,  60,  Fig.  45. 
Beekeeping,  history  of,  A.  B.,  33. 
Bees,  A.  B.,  31-43;  P.  B.,  Figs.  30, 

31. 

Beggar's  ticks,  P.  B.,  93. 
Benzine  as  used  in  testing  for  fat, 

P.  B.,  20. 
Beverages,   P.  B.,   128-130;    H.  B., 

65-75. 

Bicuspid  teeth,  H.  B.,  86. 
Bidens,  P.  B.,  93. 
Biennial,  P.  B.,  158. 
Bile,  H.  B.,  101. 
Bile  duct,  H.  B.,  101, 
Bill  of  birds,  A.  B.,  64. 
Biologists,  lives  of,  H.  B.,  168. 
Biology,  definition  of,  P.  B.,  4. 
Bird  houses,  A.  B.,  99,  Fig.  77. 
Birds,  A.  B.,  62-100. 
Bivalve,  A.  B.,  181. 
Black-leaf-40,  A.  B.,  61. 
Blade  of  leaf,  P.  B.,  55. 
Blood, 

of  frog,  A.  B.,  110. 

of  fish,  A.  B.,  131. 

of  man,  H.  B.,  7,  107. 
Blood  corpuscles, 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  7,  Fig.  5. 
Blood  flow,  stopping  of,  H.  B.f  120. 
Blood  plasma, 

composition  of,  H.  B.,  107. 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  7. 
Bobolink,  A.  B.,  79,  90,  Fig.  67. 
Bobwhite,  A.  B.,  Fig.  62. 
Body,  cell,  P.  B.,  28,  29. 
Boiling, 

meats,  H.  B.,  54. 

vegetables,  H.  B.,  55. 
Books,   list   suggested  for  reference, 

H.  B.,  207-209. 
Botany,  definition  of,  P.  B.,  4. 
Bottle,  poison,  A.  B.,  1,  Fig.  2. 
Boxes  for  insects,  A.  B.,  3,  Figs.  4,  5. 
Boys, 

as  destroyers  of  birds,  A.  B.,  92. 

as  protectors  of  birds,  A.  B.,  98. 


INDEX 


213 


Brain,  H.  B.,  155. 

Branches  of  animal  kingdom,  A.  B., 

190. 

Bread  making,  H.  B.,  55 ;  P.  B.,  148. 
Bread  mold,  P.  B.,  149-151. 
Breastbone,  H.  B.,  146,  Fig.  44. 
Breathing  capacity  of  lungs,  H.  B., 

131. 

Breathing,  definition  of ,   H.   B.,  124. 
Breathing    in    plants    and    animals, 

P.  B.,  69. 
Breathing  movements, 

of  crayfish,  A.  B.,  154. 

of  fish,  A.  B.,  134. 

of  frog,  A.  B.,  102. 

of  grasshopper,  A.  B.,  26. 

of  man,  H.  B.,  130-131. 
Breathing  pores,  A.  B.,  26,  Fig.  17. 
Breathing  tubes,  A.  B.,  26,  Fig.  17. 
Broiling  meats,  H.  B.,  54. 
Bronchial  tubes,  H.  B.,  125. 
Bronchitis,  H.  B.,  135. 
Brood  chamber,  A.  B.,  34,  Fig.  23. 
Budding  of  yeast,  P.  B.,  146,  Fig.  74. 
Buds,  P.  B.,  53. 

of  hydra,  A.  B.,  177. 

of  yeast,  P.  B.,  146. 
Bud-scales,  P.  B.,  53. 
Bud-scale  scars,  P.  B.,  55. 
Bulbs,  P.  B.,  108. 
Bullhead,  A.  B.,  Fig.  101. 
Bumblebee,  A.  B.,  31-33;  P.  B.,  81. 
Burbank,  Luther,  P.  B.,  122. 
Burdock,  P.  B.,  93. 
Burns,  treatment  of,  H.  B.,  142. 
Burs,  P.  B.,  93. 

Business  arguments  for  total  absti- 
nence, H.  B.,  74. 
Butterflies,  A.  B.,  1-22. 

Cabbage,  P.  B.,  127. 

Cabbage  butterfly,  A.  B.,  14,  Fig,  10. 

Calyx,  P.  B.,  71,  79,  88. 

Cambium,  P.  B.,  46,  51,  63. 

Camphor,  P.  B.,  129. 

Canine  teeth,  A.  B.,  188;  H.  B.,  86. 

Capillaries, 

of  fish,  A.  B.,  131. 

of  frog,  A.  B.,  103, 113,  Figs.  82,  83. 


of  man,  H.  B.,  109,  115-116,  Fig. 

36. 

Capsule  of  moss,  P.  B.,  164. 
Carbohydrates, 

composition,  P.  B.,  13,  14. 

in  human  body,  H.  B.,  44. 

manufacture  of,  P.  B.,  24,  60,  69. 

meaning  of,  P.  B.,  13,  14. 

uses  of,  in  human  body,  H.  B.,  51. 
Carbon,  P.  B.,  6. 
Carbon  dioxid,  P.  B.,  7,  8. 

excretion  of,  A.  B.,  114,  136. 

formed  by  yeast,  P.  B.,  147. 

formed  in  growing  plants,  P.  B.,  68. 

in  air,  P.  B.,  11. 

necessary  for  starch  manufacture, 
P.  B.,  23. 

production  of,  in  man,  H.  B.,  122. 
Carpet  sweeper,  use   of,   H.   B.,   26, 

Fig.  11. 

Cartilage,  H.  B.,  144. 
Castor  bean  seedling,  P.  B.,  Fig.  44. 
Catarrh,  H.  B.,  134. 
Caterpillar,  A.  B.,  11,  Fig.  6. 
Cats,  as  destroyers  of  birds,  A.  B.,  92. 
Cauliflower,  P.  B.,  127. 
Cause, 

of  diphtheria,  H.  B.,  34. 

of  pneumonia,  H.  B.,  34. 

of  tuberculosis,  H.  B.,  30. 
Cell  body,  P.  B.,  28,  29;   H.  B.,  6. 
Cell  division,  P.  B.,  30. 
Cell-nucleus,  P.  B.,  28,  29. 
Cell  sap,  P.  B.,  30. 
Cells, 

definition,  P.  B.,  30  ;  H.  B.,  6. 

division  of,  H.  B.,  6,  Fig.  4. 

of  blood,  H.  B.,  7. 

of  other  tissue,  H.  B.,  9. 

of  plants,  P.  B.,  27,  29,  Figs.  6,  7; 
H.  B.,  5,  Figs.  3,  4. 

osmosis  in,  P.  B.,  34. 
Cellulose,  P.  B.,  29;    H.  B.,  5. 
Cell  wall,  P.  B.,  28,  29. 
Cement  of  tooth,  H.  B.,  88. 
Central  cylinder  of  roots,  P.  B.,  39. 
Cephalothorax,  A.  B.,  151. 
Chalk,  A.  B.,  173. 
Charts,  price  list  of,  P.  B.,  175-176. 


214 


INDEX 


Chemicals,  price  list  of,  P.  B.,  176- 

177. 

Cherries,  P.  B.,  96. 
Chest  cavity,  H.  B.,  1,  129,  Fig.  1. 
Chestnut, 

fruits,  P.  B.,  Fig.  39. 

leaf,  P.  B.,  Fig.  20,  B. 
Chitin,  A.  B.,  45. 
Chittenden's  experiments  relative  to 

diet,  H.  B.,  61,  footnote. 
Chlorophyll,  P.    B.,    23,    28,    51,  60, 

62,  Fig.  22. 

Chlorophyll  bands,  P.  B.,  167,  Fig.  85. 
Chocolate,  P.  B.,  129,  Fig.  63  ;  H.  B., 

66. 
Chrysalis  of  butterfly,  A.  B.,  12,  Fig. 

6. 

Cider,  P.  B.,  148. 
Cilia, 

in  windpipe,  H.  B.,  126,  Fig.  18. 

of  bacteria,  H.  B.,  11. 

of  paramecium,  A.  B.,  165,  167. 
Cinchona,  P.  B.,  129. 
Circulation, 

of  fish,  A.  B.,  131,  Fig.  99. 

of  frog,  A.  B.,  110. 

of  man,  H.  B.,  107-121. 
Citranges,  P.  B.,  122. 
Clams,  A.  B.,  185. 
Classes  of  vertebrate  animals,  A.  B., 

190. 
Classification, 

of  animals,  A.  B.,  190-194. 

of  birds,  A.  B.,  73-80. 

of  invertebrates,  A.  B.,  192-193. 

of  plants,  P.  B.,  154-170. 

of  vertebrates,  A.  B.,  194. 
Clay,  P.  B.,  110. 
Clothes  moth,  A.  B.,  19,  Fig.  15. 
Clothing,  H.  B.,  143. 
Clotting  of  blood,  H.  B.,  108. 
Coagulation  of  blood,  H.  B.,  108. 
Coal,  P.  B.,  133. 

Coal  period,  forests  of,  P.  B.,  Fig.  65. 
Cocci,  H.  B.,  Fig.  7  ;  P.  B.,  Fig.  71,  A. 
Cocklebur,  P.  B.,  93. 
Cockroaches,  A.  B.,  31,  Fig.  18. 
Cocoa,  P.  B.,  129,  Fig.  63 ;   H.  B.,  66. 
Cocoon,  A.  B.,  13,  Fig.  16. 


Codfish,  A.  B.,  144-146,  Fig.  108. 
Codling  moth,  A.  B.,  18,  Fig.  14. 
Coelenterata,  A.  B.,  176. 
Coffee,  P.  B.,  129,  Fig.  61. 

effect  on  body,  H.  B.,  65. 

preparation  of,  H.  B.,  65. 

use  and  abuse  of,  H.  B.,  65. 
Cold  baths,  H.  B.,  141. 
Cold-blooded    animals,    A.    B.,    194, 

footnote. 

Colds,  H.  B.,  135. 
Collar  bones,  H.  B.,  146.  Fig.  44. 
Colony  of  bacteria,  H.  B.,  12,  Fig,  11 ; 

P.  B.,  142,  Fig.  71,  A. 
Colorado  potato  beetle,  A.  B.,  59,  Fig. 

42. 
Comb  building  of  bees,  A.  B.,  37,  Fig. 

27. 

Composition  of  the  body,  H.  B.,  44. 
Compound,  definition  of,  P.  B.,  12. 
Compound  leaf,  P.  B.,  56. 
Conditions, 

essential  for  plant  growth,  P.  B., 
108-114. 

favorable     and     unfavorable     for 

growth  of  bacteria,  H.  B.,  17. 
Conjugation  in  spirogyra,  P.  B.,  168. 
Connective  tissue,  H.  B.,  3. 
Conscious  activities,  H.  B.,  158. 
Conservation, 

of  birds,  A.  B.,  97. 

of  food  fishes,  A.  B.,  147-150. 

of  forests,  P.  B.,  138. 
Constipation,  H.  B.,  103. 
Consumption,  due  to  bacteria,  P.  B., 

145 ;  H.  B.,  30-34. 
Contractile  vacuole,  A.  B.,  169. 
Cooking  of  foods,  H.  B.,  52-56. 
Cooperation  of  organs  of  body,  H.  B., 

155. 

Corals,  A.  B.,  178,  Fig.  126. 
Corn,  cross-pollination,  P.  B.,  85. 
Corn  ears,  P.  B.,  88. 
Corn  grain,  P.  B.,  95,  128. 
Corn  grains,  P.  B.,  101. 

nutrients  stored  in,  P.  B.,  104. 

use  of  endosperm  of,  P.  B.,  104. 
Corn    production   in    United    States, 
P.  B.,  119. 


INDEX 


215 


Corn  seedling,  P.  B.,  100. 

Corn  silk,  P.  B.,  88. 

Corn  stalk,  P.  B.,  47,  49,  50. 

Corn  "tassels,"  P.  B.,  87,  Fig.  33. 

Cornea,  H.  B.,  163. 

Corolla,  P.  B.,  71,  79,  88. 

Corpuscles, 

of  frog,  A.  B.,  111.  113. 

of  man,  H.  B.,  7,    Fig.  5. 
Cortex  of  roots,  P.  B.,  39. 
Cost  of  foods,  H.  B.,  56,  Fig.  22. 
Cotton,  P.  B.,  130-132. 
Cotyledon,  P.  B.,  98,  101. 
Cough  medicines,  H.  B.,  78. 
Crab,  A.B.,  161,  Figs.  113,  114. 
Cranium,  H.  B.,  146. 
Crayfish,  A.  B.,  151-163. 
Crops,  valuable,  of  New  York  State, 

P.  B.,  122,  Fig.  58. 
Crossing,  artificial,  of  related  species, 

P.  B.,  120. 
Cross-pollination,  P.  B.,  79. 

by  bumblebees,  P.  B.,  81. 

by  insects,  P.  B.,  86. 

by  wind,  P.  B.,  87. 

in  pansy,  P.  B.,  82-84. 
Croton  bugs,  A.  B.,  31,  Fig.  18. 
Crow,  A.  B.,  88,  90,  Fig.  74. 
Crown  of  tooth,  H.  B.,  88,  Fig.  30. 
Crystalline    lens,    H.    B.,    163,    Fig. 

52. 

Cuckoo,  A.  B.,  85,  90,  frontispiece. 
Cucumber  fruit,  P.  B.,  90. 
Cultivation  of  soil,  P.  B.,  113. 
Cure  of  tuberculosis,  H.  B.,  32. 
Cuts,  treatment  of,  H.  B.,  29. 

Daily  diet,  H.  B.,  60-62. 

Dairy  products  of  New  York  State, 

P.  B.,  123. 

Dandelion  plant,  P.  B.,  Fig.  55. 
Dandruff,  H.  B.,  142. 
Dangers  to  forests,  P.  B.,  137. 
Darwin,  Charles,  P.  B.,  82,  118,  Fig. 

54. 
Deciduous  trees  and  shrubs,   P.   B., 

158. 
Decomposition,    result    of    action   of 

bacteria,  P.  B.,  140. 


Decrease  in  bird  life,  A.  B.,  91. 
Deep  sea  angler,  A.  B.,  Fig.  97. 
Defective  eyes,  H.  B.,  164. 
Dentine,  H.  B.,  89. 
Dermis,  H.  B.,  140. 
Destruction  of  birds,  A.  B.,  92-97. 

effect  of,  A.  B.,  96. 
Diaphragm,  H.  B.,  1,  131,  Fig.  1. 
Diastase,  P.  B.,  36. 
Dicptyledons,  P.  B.,  160,  170. 
Diet,  daily,  H.  B.,  60-62. 
Digestion, 

definition  of,  P.  B.,  37. 

in  crayfish,  A.  B.,  157. 

in  fish,  A.  B.,  130. 

in  frog,  A.  B.,  110. 

in  man,  H.  B.,  82-98. 

of  fats,  H.  B.,  98. 

of  insoluble  salts,  H.  B.,  95. 

of  proteins,  H.  B.,  95-96,  98. 

of  starch,  P.  B.,  37;  H.  B.,  90,  98. 
Digestive  ferments,  P.  B.,  38. 

of  fish,  A.  B.,  131. 

of  man,  H.  B.,  84. 
Digestive  glands, 

of  crayfish,  A.  B.,  157. 

of  fish,  A.  B.,  130. 

of  man,  H.  B.,  83. 
Digestive  system,  H.  B.,  82-98,  Fig. 

26. 
Diphtheria,  due  to  bacteria,   P.   B., 

145  ;  H.  B.,  34. 
Directions  for  notebooks,  H.  B.,  185— 

186. 

Direct  metamorphosis,  A.  B.,  29. 
Disease, 

prevention  of,  H.  B.,  102. 

safeguards  of  body  against,  H.  B., 

42. 
Disease-producing    bacteria,    P.    B., 

145. 
Diseases  of  respiratory  organs,  H.  B., 

134. 

Dislocations,  H.  B.,  149. 
Dispersal  of  seeds,  P.  B.,  91. 
Distal,  A.  B.,  6. 
Distillation,  P.  B.,  147. 
Distilled  liquors,  P.  B.,  148. 
Distribution  of  bacteria,  H.  B.,  16. 


216 


INDEX 


Division  of  cell,  P.  B.,  30. 
Dorsal,  A.  B.,  8. 
Drainage,  P.  B.,  Ill,  114. 
Drawings,  in  laboratory,  H.  B.,  181, 

Figs.  90,  91. 

Drone  bee,  A.  B.,  36,  Fig.  24. 
Drugs,  P.  B.,  130;  H.  B.,  78-81. 
Dry  fruits,  P.  B.,  96. 
Ducts,  P.  B.,  45,  50,  62,  Fig.  14. 
Dusting,  proper  method  of,  H.  B.,  26. 
Dustless  dusters,  H.  B.,  26. 
Dyspepsia,  H.  B.,  103. 

Ear, 

of  bird,  A.  B.,  65. 

of  man,  H.  B.,  166-167. 
Eardrum,  H.  B.,  166. 
Earthworm,  A.  B.,  179. 
Earwax,  H.  B.,  166. 
Economic  importance, 

of  bees,  A.  B.,  42. 

of  birds,  A.  B.,  83-91. 

of  butterflies  and  moths,  A.  B.,  13- 
22. 

of  Crustacea,  A.  B.,  162. 

of  fish,  A.  B.,  141-144. 

of  frogs  and  toads,  A.  B.,  118. 

of  grasshoppers,  A.  B.,  30. 

of  mammals,  A.  B.,  189. 

of  protozoa,  A.  B.,  173. 
Economy,  in  relation  to  foods,  H.  B., 

56-60. 

Eel,  A.  B.,  Fig.  96. 
Effects  of  bird  destruction,  A.  B.,  96. 
Egg  cell, 

of  bee,  A.  B.,  36. 

of  bird,  A.  B.,  70. 

of  butterfly,  A.  B.,  11. 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  137. 

of  frog,  A.  B.,  114. 

of  grasshopper,  A.  B.,  28. 

of  plants,  P.  B.,  77. 
Eggs, 

of  bee,  A.  B.,  36. 

of  butterfly,  A.  B.,  11,  Fig.  6. 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  137. 

of  frog,  A.  B.,  114,  Fig.  84. 


of  grasshopper,  A.  B.,  28,  Fig.  19. 

of  hen,  A..  B.,  69,  Figs.  52-54. 

of  house  fly,  A.  B.,  57,  Fig.  41. 

of  humming  bird,  A.  B.,  Fig.  56. 

of  lobster,  A.  B.,  Fig.  112. 

of  mosquito,  A.  B.,  43,  Figs.  31,  32. 

of  ostrich,  A.  B.,  Fig.  56. 
Egret,  A.  B.,  Fig.  75. 
Element,  definition  of,  P.  B.,  12. 
Elm  fruit,  P.  B.,  92. 
Elodea,  P.  B.,  25,  28,  Fig.  5. 
Embryo, 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  Fig.  103. 

of  frog,  A,  B.,  116,  Fig.  86. 

of  hen,  A.  B.,  70,  Figs.  52,  54. 

of  plants,  P.  B.,  77,  98,  Fig.  29. 
Enamel   of   tooth,    H.    B.,    88,    Fig. 

30. 
Endosperm,  P.  B.,  101. 

use  of,  P.  B.,  104. 
Energy, 

definition  of,  P.  B.,  64. 

liberation  of,  A.  B.,  113,  135,  158; 
P.  B.,  66,  67;    H.  B.,  123. 

source  of,  P.  B.,  66. 

transformations  of,  P.  B.,  65. 
English  sparrow,  A.  B.,  88,  97. 
Enlargement  of  chest  cavity,  H.  B., 

130. 
Epidermis, 

of  human  body,  H.  B.,  139. 

of  leaf,  P.  B.,  56,  61,  62,  Figs.  21,  22. 

of  root,  P.  B.,  44,  62. 

of  stem,  P.  B.,  51,  62. 
Epiglottis,  H.  B.,  126. 
Equipment  of  laboratory,  H.  B.,  171- 

177. 
Erosion,   as  result  of  destruction  of 

forests,  P.  B.,  137. 
Essential  organs,  P.  B.,  71,  73. 
Eustachian  tubes,  H.  B.,  167. 
Evergreen  trees  and  shrubs,   P.   B., 

158. 
Excretion, 

of  amoeba,  A.  B.,  171. 

of  paramecium,  A.  B.,  166,  169. 

of  water  in  plants,  P.  B.,  61. 
Excurrent  siphon,  A.  B.,  184. 


INDEX 


217 


Exercise,  importance  of,  H.  B.,  102, 

120,  129,  133,  151,  160. 
Existence,  struggle  for,   P.  B.,   114- 

119,  Fig.  53. 
Exodus,  A.  B.,  30. 
Expiration,  H.  B.,  124,  132. 
Extermination, 

of  house  fly,  A.  B.,  57. 

of  mosquitoes,  A.  B.,  54,  Figs.  38, 

39. 

External  ear,  H.  B.,  166. 
Eye, 

of  bee,  A.  B.,  31. 

of  bird,  A.  B.,  62. 

of  butterfly,  A.  B.,  6. 

of  crayfish,  A.  B.,  156. 

of  fish,  A.  B.,  Fig.  90. 

of  frog,  A.  B.,  104. 

of  grasshopper,  A.  B.,  22. 

of  man,  H.  B.,  162,  165. 

False  foot,  A.  B.,  170,  171. 
Family,  plant,  P.  B.,  160,  170. 
Farsightedness,  H.  B.,  164. 
Fat, 

composition  of,  P.  B.,  14,  15. 

digestion  of,  H.  B.,  98. 

in  human  body,  H.  B.,  44. 

test  for,  P.  B.,  19. 

uses  of,  H.  B.,  51. 
Feathers,  A.  B.,  67,  Figs.  49,  50. 
Feeding  of  birds,  A.  B.,  99. 
Fehling's    solution,    preparation    of, 

P.  B.,  17. 
Femur, 

of  bee,  A.  B.,  33. 

of  grasshopper,  A.  B.,  24. 
Fermentation,  P.  B.,  148. 
Ferments, 

digestive,  P.  B.,  38. 

in  fish,  A.  B.,  131. 

in  frog,  A.  B.,  110. 

in  gastric  juice,  H.  B.,  94. 

in  saliva,  H.  B.,  92. 
Ferns,  P.  B.,  161-164,  Figs.  82,  83. 
Fertilization,  P.  B.,  76,  77,  88. 

in  bees,  A.  B.,  36. 

in  bird,  A.  B.,  70. 

in  butterfly,  A.  B.,  11. 


in  fish,  A.  B.,  139. 

in  frog,  A.  B.,  114. 

in  grasshopper,  A.  B.,  28. 

of  egg  cell  in  fern,  P.  B.,  163. 
Fertilized  egg-cell,  P.  B.,  77. 
Fertilizers,  P.  B.,  114. 
Fiber-producing  plants,  P.  B.,   130- 

132. 

Fibers,  P.  B.,  47. 
Fibrous  bark,  P.  B.,  46. 
Field  work  on  birds,  A.  B.,  82. 
Filament,  P.  B.,  71,  73,  88,  Fig.  25. 
Fins, 

of  goldfish,  A.  B.,  126. 

of  other  fish,  A.  B.,  125. 

of  perch,  A.  B.,  121. 
Fire, 

lanes,  P.  B.,  139. 

wardens,  P.  B.,  139. 
Fish,  A.  B.,  120-149. 
Flamingoes,  A.  B.,  Fig.  61. 
Flavoring  extracts.  P.  B.,  128. 
Flavors, 

of  food,  P.  B.,  145. 

relation  of  bacteria  to,  H.  B.,  22. 
Flax,  P.  B.,  130. 
Fleshy  fruits,  P.  B.,  93,  96. 
Flies,  A.  B.,  57-59. 

and  typhoid  fever,  H.  B.,  37. 
Floods,  prevention  of,  P.  B.,  136. 
Floral  envelopes,  P.  B.,  71,  72,  79,  88. 
Flounder,  A.  B.,  Fig.  93. 
Flowers,  P.  B.,  70-88. 

gladiolus,  P.  B.,  72-74. 

pansy,  P.  B.,  79-82. 

tulip,  P.  B.,  70-72. 
Fly-catchers,  A.  B.,  80,  Fig.  69. 
Food,  definition  of,  H.  B.,  46. 
Food  economy,  H.  B.,  56-60. 
Food  getting, 

of  amoeba,  A.  B.,  171. 

of  bee,  A.  B.,  32,  39. 

of  butterfly,  A.  B.,  7,  11. 

of  crayfish,  A.  B.,  157. 

of  fish,  A.  B.,  128. 

of  frog,  A.  B.,  104,  110. 

of  hydra,  A.  B.,  177. 

of  mussel,  A.  B.,  182. 

of  paramecium,  A.  B.,  165,  168. 


218 


INDEX 


Foods,  H.  B.,  44-63. 

and  the  blood,  H.  B.,  108. 

and  the  muscles,  H.  B.,  151. 

and  the  nervous  system,  H.  B.,  160. 

and  the  skeleton,  H.  B.,  147. 
Food  substances, 

in  corn  grains,  P.  B.,  104. 

in  human  body,  H.  B.,  44. 

list  of,  P.  B.,  13. 

manufacture  by  plants,  P.  B.,  22, 
60. 

storage  of,  P.  B.,  61. 

transfer  of,  P.  B.,  50. 
Foot, 

of  grasshopper,  A.  B.,  24. 

of  mussel,  A.  B.,  182. 
Forest  conservation,  P.  B.,  138. 
Forest  fires,  P.,B.,  134,  137,  139. 
Forests,  dangers  to,  P.  B.,  137. 
Formalin  as  food  preservative,  H.  B., 

24,  footnote. 

Fossil  bird,  A.  B.,  Fig.  47. 
Fractures,  H.  B.,  148. 
Fresh  air,  importance  of,  H.  B.,  33, 

129,  151,  160. 
Frogs,  A.  B.,  101-119. 
Fronds  of  ferns,  P.  B.,  161. 
Frosts,  loss  of  crops  due  to,  P.  B.,  117. 
Fruit, 

definition  of,  P.  B.,  94. 

hybrid,  P.  B.,  122. 

stalk,  P.  B.,  91,  92. 
Fruits,  P.  B.,  89-96. 
Frying,  H.  B.,  53. 
Fuel,  P.  B.,  133. 
Function  of  organ,  H.  B.,  2. 
Functions  of  organs,  P.  B.,  27. 
Fungi,    relation    to    human    welfare, 

P.  B.,  139-153. 
Fungous  diseases,  loss  of  crops  due 

to,  P.  B.,  117. 
Furnace  heat,  H.  B.,  138. 

Gall  bladder,  H.  B.,  101,  Fig.  2. 
Garden, 

glass-plate,  P.  B.,  102. 

tumbler,  P.  B.,  102. 
Gastric  glands,  H.  B.,  93,  Fig.  31. 
Gastric  juice,  H.  B.,  93. 


Generations,  alternation  of,  in  fern, 

P.  B.,  163. 

Generative  nucleus,  P.  B.,  77. 
Genus,  plant,  P.  B.,  160,  170. 
Germination  of  pollen  grains,  P.  B., 

76. 

Germs,  H.  B.,  23,  footnote. 
Gill  arch,  A.  B.,  133. 
Gill  bailer,  A.  B.,  155. 
Gill  chamber,  A.  B.,  155. 
Gill  clefts,  A.  B.,  132. 
Gill  cover, 

of  gold  fish,  A.,  B.  122. 

of  perch,  A.  B.,  121. 
Gill  filaments, 

of  crayfish,  A.  B.,  154. 

of  fish,  A.  B.,  133. 
Gill  rakers,  A.  B.,  133. 
Gill  teeth,  A.  B.,  133. 
Gills, 

of  crayfish,  A.  B.,  153, 158,  Fig.  111. 

of  fish,  A.  B.,  132-134. 

of  mussel,  A.  B.,  183. 

of  tadpole,  A.  B.,  116. 
Girls,  as  protectors  of  birds,  A.  B.,  99. 
Gladiolus,  P.  B.,  72-74. 
Glands, 

of  intestine,  H.  B.,  97. 

of  mouth,  H.  B.,  91. 

of  skin,  H.  B.,  140. 

of  stomach,  H.  B.,  95. 
Glass-plate  garden,  P.  B.,  102. 
Glottis, 

of  frog,  A.  B.,  101. 

of  man,  H.  B.,  125. 
Goddard,    Miss    Martha   F.,    P.    B., 

193. 

Grafting,  P.  B.,  105-106. 
Grapes,  P.  B.,  129. 
Grape  sugar, 

composition  of,  P.  B.,  14,  15. 

osmosis  of,  P.  B.,  33.^ 

test  for,  P.  B.,  16. 
Grasshoppers,  A.  B.,  22-31. 
Gravel,  P.  B.,  110. 
Gray  matter  of  nervous  system,  H.  B., 

157. 

Grazing  animals,  a  danger  to  young 
trees,  P.  B.,  137. 


INDEX 


219 


Growth,  necessity  of  foods  for,  H.  B., 

45. 

Growth  of    crystals,  P.  B.,  2,  foot- 
note. 

Growth  of  living  things,  P.  B.,  2,  30. 
Growth  of  plants,  five  essential  con- 
ditions for,  P.  B.,  108. 
Guard-cells  of  stoma,  P.  B.,  58,  61,  62, 

Fig.  21. 

Gull,  A.  B.,  Fig.  59. 
Gullet, 

of  fish,  A.  B.,  130. 
of  frog,  A.  B.,  108. 
of  man,  H.  B.,  92. 
of  paramecium,  A.  B.,  165. 
Gymnosperms,  P.  B.,  159,  170. 
Gypsy  moth,  A.  B.,  16,  Fig.  13. 

Habit,  importance  of,  H.  B.,  159. 
Habits,  hygienic, 

of  breathing,  H.  B.,  132. 

of  eating,  H.  B.,  102. 
Habitual  activities,  H.  B.,  158. 
Hair,  care  of,  H.  B.,  141. 
Harrow,  P.  B.,  114,  Fig.  51. 
Hatchery,  A.  B.,  141. 
Hawk,  A.  B.,  78,  87,  89,  91,  Fig.  64. 
Hay  crop  of  New  York  State,  P.  B., 

122. 

Headache  powders,  H.  B.,  78. 
Heart, 

of  fish,  A.  B.,  131,  Fig.  100. 

of  frog,  A.  B.,  107,  111. 

of  man,  H.  B.,  1,  109. 
Heat, 

energy,  P.  B.,  64. 

relation  of,  to  soil,  P.  B.,  112. 

production  of,  in  man,  H.  B.,  122. 
Hemoglobin,  H.  B.,  128. 
Hemp,  P.  B.,  130,  145. 
Hen,  egg  of,  A.  B.,  Figs.  52,  54,  56. 
Herb,  P.  B.,  156,  Fig.  80. 
Heron,  A.  B.,  Fig.  60. 
Herring,  A.  B.,  Fig.  110. 
Herring  gull,  A.  B.,  Fig.  59. 
High  school  education,  value  of,  P.  B., 

124. 

Hilum,  P.  B.,  97. 
Hodge,  Professor  C.  F., 


experiments  on  dogs,  H.  B.,  68-72. 

extermination  of  house  fly,  A.  B., 

59. 

Honeybees,  A.  B.,  33-41. 
Honey,  making,  A.  B.,  39. 
Honey  stomach,  A.  B.,  39,  Fig.  28. 
Hoof,  A.  B.,  188. 
Horse,  A.  B.,  Fig.  137. 
Horse-chestnut, 

leaves,  P.  B.,  Fig.  20,  K. 

stem,  P.  B.,  45,  52. 
House  fly,  A.  B.,  57,  58,  Fig.  40,  41. 
House  mosquito,  A.  B.,  43. 
Human  welfare,  relation  of  plants  to, 

P.  B.,  126-153. 

Humming  bird,  egg  of,  A.  B.,  Fig.  56. 
Humus,  P.  B.,  111. 
Hybrid  fruits,  P.  B.,  122. 
Hydra,  A.  B.,  176,  Figs.  124,  125. 
Hydrogen,  P.  B.,  9. 
Hydrophobia,  H.  B.,  41,  170. 
Hygiene, 

of  blood,  H.  B.,  108. 

of  circulation,  H.  B.,  119-121. 

of  digestion,  H.  B.,  102-105. 

of  eyes,  H.  B.,  165. 

of  muscles,  H.  B.,  151. 

of  nervous  system,  H.  B.,  160. 

of  red  corpuscles,  H.  B.,  128. 

of  respiratory  organs,  H.  B.,  132. 

of  teeth,  H.  B.,  89. 
Hyptue  of  molds,  P.  B.,  150. 
Hypocotyl,  P.  B.,  98. 

Importance  of  birds  to  man,  A.  B., 

83-91. 
Importance  of  proper  cooking,  H.  B., 

52. 
Improvement  of  plants  by  man,  P.  B., 

119-125,  Figs.  57,  59. 
Incisor  teeth,  A.  B.,  188;    H.  B.,  86. 
Incomplete    metamorphosis,    A.    B., 

29. 

Incurrent  siphon,  A.  B.,  184. 
Indigestible     foods,     avoidance     of, 

H.  B.,  62. 

Indigo,  preparation  of,  P.  B.,  145. 
Infantile  paralysis,  H.  B.,  41. 
Injurious  birds,  A.  B.,  88. 


220 


INDEX 


Injurious  effects  of  bacteria,  H.  B.,  23. 
Insecticides,  A.  B.,  61. 
Insect  net,  A.  B.,  1,  Fig.  1. 

boxes,  A.  B.,  3,  Fig.  5. 

collections,  A.  B.,  Fig.  4. 

killing  bottle,  A.  B.,  1,  Fig.  2. 

spreading  board,  A.  B.,  2,  Fig.  3. 
Insects,  A.  B.,  1-61. 

a  danger  to  forests,  P.  B.,  137. 

additional  topics,  A.  B.,  59—61. 

bees,  A.  B.,  31-43. 

butterflies  and  moths,  A.  B.,  1-22. 

destruction  of,  by  birds,  A.  B.,  84. 

flies,  A.  B.,  57-59. 

grasshoppers,  A.  B.,  22-31. 

loss  of  crops  due  to,  P.  B.,  117. 

mosquitoes,  A.  B.,  43-57. 

moths,  A.  B.,  13-22. 
Insoluble  salts,  H.  B.,  94. 
Inspiration,  H.  B.,  124,  130,  131. 
Intemperance,  cost  of,  H.  B.,  75. 
Intestinal  glands,  H.  B.,  97. 
Intestine, 

of  fish,  A.  B.,  130,  Fig.  98. 

of  frog,  A.  B.,  108,  110,  Fig.  80. 

of  man,  H.  B.,  2,  97,  Fig.  26. 
Invertebrates,  A.  B.,  190,  192,  193. 
Involuntary  muscles,  H.  B.,  94,  151. 
Iodine  solution,  preparation,  P.  B.,  15. 
Iris, 

of  fish,  A.  B.,  62. 

of  man,  H.  B.,  163. 
Irrigation,  P.  B.,  111. 
Isinglass,  A.  B.,  142. 

Jaundice,  H.  B.,  102. 
Jellyfish,  A.  B.,  Fig.  127. 
Jenner,  Dr.  Edward,  H.  B.,  40. 
Joint,  H.  B.,  147,  Fig.  45. 
Jungle  fowl,  A.  B.,  Fig.  63. 
Jute,  P.  B.,  145. 

Katydids,  A.  B.,  31. 
Kerosene,  P.  B.,  133. 

emulsion  of,  A.  B.,  61. 

treatment  for  mosquitoes,  A.  B.,  55. 
Kingbird,  A.  B.,  Fig.  69. 
Kingfisher,  A.  B.,  73,  Fig.  58. 
Koch,  Sir  Robert,  H.  B.,  30,  Fig.  13. 


Labial  palps, 

of  bee,  A.  B.,  32. 

of  butterfly,  A.  B.,  7. 

of  grasshopper,  A.  B.,  23. 
Laboratory, 

equipment,  H.  B.,  171-177. 

table,  H.  B.,  171. 
Labrum,  A.  B.,  23,  Fig.  18. 
Large  intestine,  H.  B.,  98. 

absorption  in,  H.  B.,  101. 
Larva, 

of  bee,  A.  B.,  40,  Fig.  29. 

of  butterfly,  A.  B.,  12,  Fig.  6. 

of  mosquito,  A.  B.,  43,  Figs.  31,  32. 
Larynx,  H.  B.,  125. 
Lateral  buds,  P.  B.,  53. 
Lateral  line,  A.  B.,  137. 
Layer,  P.  B.,  106. 

Laws  relating  to  bird  protection,  A. 
B.,  97. 

to  protection  of  fish,  A.  B.,  150. 
Lazear,  Dr.  Jesse,  A.  B.,  51,  Fig.  35. 
Leaflets,  P.  B.,  56. 
Leaf  scars,  P.  B.,  53. 
Leaf -stalk,  P.  B.,  55. 
Leaves, 

arrangement  of,  P.  B.,  52. 

structure  of,  P.  B.,  55. 
Leg,    skeleton    of,    A.    B.,    Fig.    51 ; 

H.  B.,  146,  Fig.  44. 
Lenticels,  P.  B.,  51,  55,  62. 
Lepidoptera,  A.  B.,  10. 
Lettuce,  P.  B.,  127. 
Life  history, 

of  a  seed  plant,  P.  B.,  195. 

of  bee,  A.  B.,  40,  Fig.  29. 

of  bird,  A.  B.,  70. 

of  butterfly,  A.  B.,  10-12,  Fig.  6. 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  137,  Fig.  103. 

of  frog,  A.  B.,  114,  Fig.  84. 

of  grasshopper,  A.  B.,  28,  Figs.  19, 
20. 

of  house  fly,  A.  B.,  57,  Fig.  41. 

of  house  mosquito,  A.  B.,43,  Fig.  31. 

of  malaria-transmitting  mosquito, 

A.  B.,  46,  Fig.  32. 
Life  insurance  and  total  abstinence, 
H.  B.,  73. 


INDEX 


221 


Lifeless  things,  characteristics  of,  P. 

B.,  1. 

Lilac  leaf,  P.  B.,  Fig.  20,  A. 
Limewater,  preparation  of,  P.  B.,  5. 
Linden  fruit,  P.  B.,  91. 
Linen, 

action  of  bacteria  in  preparation 
of,  H.  B.,  22. 

preparation  of,  P.  B.,  145. 
Liver, 

of  fish,  A.  B.,  131,  Fig.  98. 

of  frog,  A.  B.,  108,  110,  Fig.  80. 

of  man,  H.  B.,  101,  102,  Fig.  2. 
Living  things,   characteristics  of,   P. 

B.,  1. 

Lizard,  A.  B.,  Fig.  134. 
Locomotion, 

of  amceba,  A.  B.,  170,  171. 

of  birds,  A.  B.,  63,  66. 

of  butterfly,  A.  B.,  8. 

of  crayfish,  A.  B.,  151,  152. 

of  earthworm,  A.  B.,  179. 

of  fish,  A.  B.,  125-127. 

of  frog,  A.  B.,  106. 

of  grasshopper,  A.  B.,  25. 

of  hydra,  A.  B.,  177,  Fig.  125. 

of  mussel,  A.  B.,  182. 

of  paramecium,  A.  B.,  166. 
Loss  due  to  insect  pests,  A.  B.,  60. 
Louse,  A.  B.,  60,  Fig.  44. 
Lower  lip,  A.  B.,  23,  Fig.  18. 
Lumber,  P.  B.,  133. 
Lumbering, 

right  method  of,  P.  B.,  Fig.  68. 

wrong  method  of,  P.  B.,  Fig.  67. 
Lungs, 

of  frog,  A.  B.,  103. 

of  man,  H.  B.,  2,  127,  Figs.  2,  40. 

Mackerel,  A.  B.,  Fig.  95. 
Malaria,  A.  B.,  47,  174. 

transmission  of,  A.  B.,  48;  H.  B., 

42. 

Malaria  parasite,  A.  B.,  49. 
Malaria-transmitting  mosquito,  A.  B. 

46,  174,  Fig.  32. 
Malt,  P.  B.,  148. 
Mammals,  A.  B.,  187-190. 
Mammary  glands,  A.  B.,  187. 


Mandibles, 

of  bee,  A.  B.,  33. 

of  bird,  A.  B.,  65. 

of  crayfish,  A.  B.,  156. 

of  grasshopper,  A.  B.,  23, 27. 
Mantle  of  mollusk,  A.  B.,  183. 
Maple, 

fruit,  P.  B.,  91. 

sugar,  P.  B.,  136. 
Maxilla, 

of  bee,  A.  B.,  32. 

of  crayfish,  A.  B.,  155. 

of  grasshopper,  A.  B.,  24,  27. 
Maxillary  palps,  A.  B.,  23,  Fig.  18. 
Meats, 

composition  of,  H.  B.,  Fig.  19. 

cooking  of,  H.  B.,  52-54. 
Medicines,  P.  B.,  129,  130. 
Medullary  rays,  P.  B.,  47,  50,  Fig. 

17. 

Menhaden,  A.  B.,  142. 
Mesophyll,  P.  B.,  57,  60. 
Metamorphosis,  A.  B.,  29. 

of  frog,  A.  B.,  116. 
Microbes,  H.  B.,  23,  footnote. 
Microorganisms,  H.  B.,  10-43. 
Micropyle,  P.  B.,  76,  98,  Fig.  29. 
Middle  ear,  H.  B.,  167. 
Migration  of  birds,  A.  B.,  80. 
Milk,    food    substances    present    in, 

H.  B.,  46. 

Milk  supplies,  H.  B.,  38. 
Milk  teeth,  H.  B.,  87. 
Milkweed  fruit  and  seeds,  P.  B.,  92, 

Fig.  36. 
Millinery    purposes,    destruction    of 

birds  for,  A.  B.,  94. 
Mineral  matter, 

digestion  of,  H.  B.,  95. 

in  human  body,  H.  B.,  45. 

test  for,  P.  B.,  20. 

uses  of,  H.  B.,  52. 

Mixed  diet,  necessity  for,  H.  B.,  61. 
Mixture,  definition  of,  P.  B.,  12. 
Moisture, 

effect  on  growth  of  bacteria,  H.  B., 
19. 

relation  to  germination  and  growth, 
P.  B.,  108-109. 


222 


INDEX 


Molar   teeth,    A.    B.,    188;    H.    B., 

86. 
Mold, 

bread,  P.  B.,  149-151,  Fig.  75. 

vegetable,  P.  B.,  111. 
Mollusca,  A.  B.,  181-185. 
Molting, 

of  caterpillar,  A.  B.,  12. 

of  crayfish,  A.  B.,  159. 

of  grasshopper,  A.  B.,  29. 

of  mosquito,  A.  B.,  43.  . 

Monocotyledons,  P.  B.,  159,  160,  170. 
Moran,  John,  A.  B.,  52,  54. 
Mosquitoes,  A.  B.,  43-56. 

as  a  means  of  transmitting  malaria, 
A.  B.,  48. 

as  a  means  of  transmitting  yellow 

fever,  A.  B.,  50. 
Mosses,  P.  B.,  164-166,  Fig.  84. 

moss  plant,  P.  B.,  164. 

protonema,  P.  B.,  164. 
Moths,  characteristics  of,  A.  B.,  13. 
Mouth,  absorption  in,  H.  B.,  99. 
Mouth  cavity  and  its  function,  H.  B., 

84-92,  Fig.  27. 
Muscles, 

of  bird's  wing,  A.  B.,  66. 

of  man,  H.  B.,  150-154. 
Muscular   energy,    A.   B.,    127,    158; 

H.  B.,  123. 

Mushrooms,  P.  B.,  151,  Fig.  76. 
Mussel,  A.  B.,  181-184. 

Nails,  care  of,  H.  B.,  142. 
Narcotics,  definition,  H.  B.,  64. 
Nearsightedness,  H.  B.,  164. 
Necessity  for  foods,  H.  B.,  45. 
Neck  of  tooth,  H.  B.,  89,  Fig.  30. 
Nectar,  P.  B.,  80. 
Necturus,  A.  B.,  Fig.  89. 
Nerve  centers,  H.  B.,  155. 
Nerve  fibers,  H.  B.,  155. 
Nerve  impulses,  H.  B.,  157. 
Nervous  energy,  H.  B.,  123 
Nervous  system,  H.  B.,  154-162. 
Nests 

of  birds,  A.  B.,  72,  Fig.  73. 

of  stickleback,  A.  B.,  Fig.  104. 
Net,  insect,  A.  B.,  1. 


Nettling  cells,  A.  B.,  177. 

Newt,  A.  B.,  118, 

Nitric  acid,  test  for  protein,  P.  B.,  18. 

Nitrogen,  P.  B.,  11. 

Nose  cavity,  H.  B.,  125,  Fig.  39. 

Nostrils, 

of  bird,  A.  B.,  62. 

of  fish,  A.  B.,  136. 

of  frog,  A.  B.,  101. 
Notebooks   in   biology,  H.    B.,  181- 

187. 
Nucleus,   P.   B.,   28,   29;    H.   B.,   6, 

Fig.  4. 

Nutrients,  H.  B.,  47,  footnote. 
Nutrition, 

in  fungi,  P.  B.,  150. 

in  green  plants  that  produce  seeds, 

P.  B.,  194. 
Nutritive  hypha?,  P.  B.,  150, 

organs  of  plants,  P.  B.,  39. 

Oak, 

leaves,  P.  B.,  Fig.  20,  C,  G. 

tree,  amount  of  evaporation  from, 
P.  B.,  136. 

wood,  P.  B.,  46. 
Oil  glands,  H.  B.,  140. 
Opium,  P.  B.,  129. 
Opposite  arrangement,  P.  B.,  52. 
Orange  crop,  P.  B.,  120-122. 
Order  of  topics,  H.  B.,  178-180. 
Organ,  definition,  H.  B.,  2;    A.  B., 

173. 
Organs, 

nutritive,  P.  B.,  39. 

of  a  plant,  P.  B.,  27. 

of  circulation,  H.  B.,  108-118. 

of  digestion,  H.  B.,  82-98. 

of  human  body,  H.  B.,  1. 

of  respiration,  H.  B.,  125-132. 
Osmosis,  P.  B.,  32-38. 

definition  and  applications,  P.  B., 
35. 

in  living  cells,  P.  B.,  34. 

in  root-hairs,  P.  B.,  44. 

of  grape  sugar,  P.  B.,  33. 

of  starch,  P.  B.,  35. 

protein,  P.  B.,  37. 

water,  P.  B.,  33. 


INDEX 


223 


Ostrich, 

bones  of  leg,  A.  B.,  48. 

bones  of  wing,  A.  B.,  Fig.  48. 

egg,  A.  B.,  51. 
Ovary,  P.  B.,  72,  73,  81,  88. 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  137,  Fig.  98. 

of  frog,  A.  B.,  114. 

of  hen,  A.  B.,  70,  Fig.  54. 
Ovipositor,  A.  B.,  28. 
Ovules,  P.  B.,  72,  74. 
Owls,  A.  B.,  78,  87,  90,  Fig.  65. 
Oxidation, 

definition  of,  P.  B.,  13. 

in  crayfish,  A.  B.,  158. 

in  fish,  A.  B.,  135. 

in  frog,  A.  B.,  114. 

in  man,  H.  B.,  46,  122. 

liberation  of  energy  by,  P.  B.,  66. 

relation    of    oxygen    and    carbon 

dioxid  to,  P.  B.,  67. 
Oxygen,  P.  B.,  6. 

distribution  of,  H.  B.,  128. 

given  off  by  green  plants  in  sun- 
light, P.  B.,  25. 

necessity  for,  H.  B.,  123. 

necessity  of,  for  growth,  P.  B.,  67. 

supply  of,  for  animals,  P.  B.,  25. 
Oysters,  A.  B.,  185. 

Palmately  compound,  P.  B.,  56. 
Pancreas, 

of  frog,  A.  B.,  108,  110,  Fig.  80. 
of  man,  H.  B.,  2,  98. 
Pansy,  P.  B.,  79-82. 

Darwin's  experiments  with,  P.  B., 

82-84. 

Papillae  of  tongue,  H.  B.,  85. 
Paramecium,    A.    B.,    164-170,    Fig. 

118. 

Parsnips,  P.  B.,  127,  156. 
Pasteur,   Louis,   H.   B.,  frontispiece, 

168-170. 

Pasteurization  of  milk,  H.  B.,  17,  39. 
Pasteurizers,  H.  B.,  17,  Fig.  8. 
Pasteur  treatment  for  hydrophobia, 

H.  B.,  41. 

Patent  medicines,  H.  B.,  78-81,  Figs. 
24,  25. 


Pea, 

flower,  P.  B.,  Fig.  35. 

fruit,  P.  B.,  89,  Figs.  35,  43. 
Peaches,  P.  B.,  96,  128. 
Pelican,  A.  B.,  73,  Fig.  57. 
Peppermint,  P.  B.,  129. 
Peptone,  H.  B.,  96. 
Perch,  A.  B.,  121,  Fig.  90. 
Perching  birds,  A.  B.,  79. 
Perennials,  P.  B.,  158. 
Peritoneum,  H.  B.,  97. 
Peritonitis,  H.  B.,  97. 
Permanent  residents,  A.  B.,  80. 
Permanent  teeth,  H.  B.,  88. 
Perspiratory  glands,  H.  B.,  140,  Fig. 

43. 

Petals,  P.  B.,  71,  79,  88. 
Petri  dishes,  H.  B.,  14,  Fig.  11. 
Phoebe,  A.  B.,  90. 
Pinnately  compound,  P.  B.,  56. 
Pipefish,  A.  B.,  Fig.  92. 
Pistil,  P.  B.,  71,  73,  81,  88,  Figs.  24, 

28. 
Pistillate  flowers,  P.  B.,  87,  Figs.  32, 

B,  34. 
Pith,  P.  B.,  46,  47,  63. 

rays,  P.  B.,  47,  63. 
Placenta,  P.  B.,  89. 
Plant, 

family,  P.  B.,  160,  170. 

genus,  P.  B.,  160,  170. 

species,  P.  B.,  161,  170. 

variety,  P.  B.,  161,  170. 
Plants, 

cells,  P.  B.,  27. 

manufacture  of  food  by,  H.  B.,  51. 

microscopic  structure,  P.  B.,  27. 

nutritive  organs,  P.  B.,  39. 

organs  and  functions,  P.  B.,  27. 

parts  of,  P.  B.,  26-31. 
Plasma,  H.    B.,  7. 

composition  of,  H.  B.,  107. 
Pleura,  H.  B.,  129. 
Pleurococcus,  P.  B.,  169,  Fig  86. 
Plow,  P.  B.,  113,  Fig.  50. 
Plumule,  P.  B.,  98. 
Pneumonia,  H.  B.,  34,  135. 
Poison  bottle,  A.  B.,  1. 
Pollen,  P.  B.,  71,  73,  Fig.  26. 


224 


INDEX 


Pollen  basket,  A.  B.,  33,  Fig.  26. 

Pollen  tubes,  P.  B.,  75,  Figs.  26,  27. 

Pollination,  P.  B.,  74,  76,  88.  . 

Pond  scum,  P.  B.,  166. 

Poppy,  P.  B.,  129. 

Porifera,  A.  B.,  175. 

Posterior,  A.  B.,  6. 

Potato  crop  of  New  York  State,  P.  B., 

122. 

Potatoes,  P.  B.,  107,  127,  Fig.  49. 
Preparations  for  laboratory,  H.   B., 

175. 

Preservation  of  food,  H.  B.,  23. 
Pressure,  effect  of,  on  bones,  H.  B., 

148,  Fig.  46.  *$ 

Prevention, 

of  diphtheria,  H.  B.,  36. 

of  self-pollination,  P.  B.,  84,  85. 

of  tuberculosis,  H.  B.,  32 

of  typhoid  fever,  H.  B.,  37. 
Primary  root,  P.  B.,  100. 
Proboscis,  A.  B.,  6,  10. 
Production   of   energy,    necessity   of 

foods  for,  H.  B.,  45. 
Proper  posture,  H.  B.,  153,  Figs.  48, 

49. 

Propolis,  A.  B.,  40. 
Protective  resemblance, 

of  crayfish,  A.  B.,  157. 

of  toad,  A.  B.,  Fig.  87. 

of  walking  stick,  A.  B.,  31. 
Protein, 

composition  of,  P.  B.,  14,  15. 

manufacture  of,  P.  B.,  24,  61. 

osmosis,  P.  B.,  37. 

test  for,  P.  B.,  18. 

use  of  term,  P.  B.,  13,  footnote. 
Protection  of  forests,  P.  B.,  138,  139. 
Proteins, 

digestion  of,  H.  B.,  95,  96,  98. 

in  human  body,  H.  B.,  44. 

uses  of,  H.  B.,  51. 

Prothallus  of  fern,  P.  B.,  162,  Fig.  83. 
Protonema  of  moss,  P.  B.,  164. 
Protoplasm,  P.  B.,  30;    H.  B.,  5. 
Protozoa,  A.  B.,  172. 
Proximal,  A.  B.,  6. 
Pseudopods,  A.  B.,  170,  171. 
Pulp  cavity,  H.  B.,  89. 


Pulse,  H.  B.,  112,  114. 

Pumpkin,  cross-pollination,  P.  B.,  85. 

Pupa, 

of  bee,  A.  B.,  41,  Fig.  29. 

of  butterfly,  A.  B.,  12,  Fig.  6. 

of  mosquito,  A.  B.,  44,  Figs.  31,  32. 
Pupil  of  eye, 

of  bird,  A.  B.,  62. 

of  man,  H.  B.,  163. 
Purchase  of  foods,  economy  in,  H.  B., 

58. 
Pure  Food  and  Drug  Law,  H.  B.,  24, 

81. 

Pus,  H.  B.,  29. 
Pylorus,  H.  B.,  93. 

Quail,  A.  B.,  90,  Fig.  62. 
Quartered  oak,  P.  B.,  47. 
Queen-bee,  A.  B.,  35,  Fig.  24. 
Quinine,  P.  B.,  129. 

Radiometer,  P.  B.,  66,  footnote. 
Rainfall,  regulation  of,  P.  B.,  136. 
Raspberry  fruits,  P.  B.,  Fig.  40. 
Rats  and  mice  destroyed  by   birds, 

A.  B.,  87,  Fig.  64. 
Reasons   for   cooking   animal   foods, 
H.  B.,  52. 

for  cooking  vegetables,  H.  B.,  54. 
Red  corpuscles, 

of  frog,  A.  B.,  Ill,  113. 

of  man,  H.  B.,  8,  128,  Fig.  5. 
Reed,  Dr.  Walter,  A.  B.,  50,  Fig.  34. 
Reference   books,   list  of,   suggested, 

H.  B.,  207-209. 
Reflex  activities,  H.  B.,  158. 
Reforesting,  P.  B.,  138. 
Regions  of  body,  H.  B.,  1. 
Relatives, 

of  bees,  A.  B.,  43. 

of  grasshoppers,  A.  B.,  31. 
Repair,  necessity  of  food  for,  H.  B., 

45. 

Repair  of  living  things,  P.  B.,  2. 
Reproduction, 

in  plants,  P.  B.,  70-96. 

of  amoeba,  A.  B.,  Fig.  172. 

of  bacteria,  H.  B.,  12,  Fig.  7. 

of  bee,  A.  B.,  36. 


INDEX 


225 


Reproduction, 

of  bird,  A.  B.,  70. 

of  butterfly,  A.  B.,  11. 

of  crayfish,  A.  B.,  159. 

of  fish,  A.  B.,  37. 

of  frog,  A.  B.,  114. 

of  grasshopper,  A.  B.,  28. 

of  house  fly,  A.  B.,  57. 

of  living  things,  P.  B.,  3. 

of.  mammals,  A.  B.,  190. 

of  mosquito,  A.  B.,  43. 

of  paramecium,  A.  B.,  169. 

of  reptiles,  A.  B.,  185. 
Reproductive  hyphae  of  molds,  P.  B., 

150. 

Reptiles,  A.  B.,  185-187. 
Respiration,  definition,  P.  B.,  68,  69. 

of  crayfish,  A.  B.,  158. 

of  fish,  A.  B.,  135. 

of  frog,  A.  B.,  113. 

of  man,  H.  B.,  122-138. 

of  paramecium,  A.  B.,  168. 
Retina,  H.  B.,  163. 
Review, 

of  digestion,  H.  B.,  105,  106. 

of  foods,  H.  B.,  62,  63. 
Review  topics,  H.  B.,  188-206. 
Rhizoids  of    ferns,  P.    B.,   163,   Fig. 

83,  C. 

Rhizome  of  fern,  P.  B.,  162,  Fig.  82. 
Ribs,  H.  B.,  146,  Fig.  44. 
Rind,  P.  B.,  47. 
Roasting  meats,  H.  B.,  54. 
Robin,  A.  B.,  85,  90,  Fig.  71. 

eggs,  A.  B.,  73. 
Roe,  A.  B.,  142. 
Root-hairs,  P.  B.,  40,  Figs.  11,  12,  13. 

osmosis  in,  P.  B.,  44. 
Root  of  tooth,  H.  B.,  88,  Fig.  30. 
Roots, 

aerial,  P.  B.,  102. 

functions  of,  P.  B.,  41-43. 

primary,  P.  B.,  100. 

secondary,  P.  B.,  100. 

structure  of,  P.  B.,  39-41. 
Root-tip,  P.  B.,  40. 
Root  tubercles,  P.  B.,  144,  Fig.  72. 

bacteria  in,  P.  B.,  Fig.  73. 
Rotation  of  crops,  P.  B.,  124. 


Runner,  P.  B.,  106. 
Rusts,  P.  B.,  152. 

Safeguards  of  body  against  disease, 

H.  B.,  42. 

Saliva,  H.  B.,  90-92. 
Salivary  glands,  H.  B.,  91. 
Salmon,  A.  B.,  142-144,  Fig.  107. 
Sand,  P.  B.,  110. 

San  Jose  scale,  A.  B.,  59,  Fig.  43. 
Sap,  of  cell,  P.  B.,  30. 

path  through  leaves,  P.  B.,  59. 

path  through  roots,  P.  B.,  42,  43. 

path  through  stem,  P.  B.,  48,  49. 
Scales  of  butterfly,  A.  B.,  9,  Figs.  7,  8. 
Scarlet  fever,  H.  B.,  41. 
Scavengers,  birds  as,  A.  B.,  87. 
Schleiden  and  Schwann,  P.  B.,  29; 

H;  B.,  5. 

Science  and  its  subdivisions,  P.  B.,  3. 
Scion,  P.  B.,  105. 
Scratching  birds,  A.  B.,  77,  Figs.  62, 

63. 

Sea  horse,  A.  B.,  Fig.  91. 
Sea  weeds,  P.  B.,  169. 
Secondary  root,  P.  B.,  100. 
Seed-coat,  P.  B.,  98. 
Seed  dispersal,  P.  B.,  91-94. 
Seed  leaves,  P.  B.,  98. 
Seed-producing  plants,   P.   B.,    159- 

161. 
Seedlings,  comparison  of,  P.  B.,  103, 

104. 
Seeds,  P.  B.,  72,  74,  77,  97-105. 

numbers,  produced  by  plants,   P. 

B.,  115. 

Segments,  A.  B.,-9. 
Selection,  artificial,  P.  B.,  119. 
Self-pollination,  P.  B.,  79. 

prevention  of,  P.  B.,  84-86. 
Sensations, 

of  sight,  H.  B.,  164. 

of  sound,  H.  B.,  167. 
Sepals,  P.  B.,  71,  79,  88. 
Serum  with  antitoxin,  H.  B.,  35. 
Sexual  generation, 

in  fern,  P.  B.,  163. 

in  moss,  P.  B.,  164,  166. 
Shad,  A.  B.,  Fig.  109. 


226 


INDEX 


Shaft  of  feather,  A.  B.,  67,  Fig.  50. 

Sheath  leaf,  P.  B.,  100. 

Shoulder  blades,  H.  B.,  146,  Fig.  44. 

Shower  baths,  H.  B.,  141. 

Shrimp,  A.  B.,  Fig.  116. 

Shrub,  P.  B.,  156,  Fig.  79. 

Sieve  tubes,  P.  B.,  50,  62,  Fig.  16. 

Silkworms,  A.  B.,  20,  Fig.  16. 

Siphons  of  mollusk,  A.  B.,  184. 

Skeleton,  H.  B.,  144-150,  Fig.  44. 

Skeleton  of  arm  of  man  and  wing  of 

ostrich,  A.  B.,  Fig.  48. 
Skeleton  of  leg  of  man  and  of  os- 
trich, A.  B.,  68,  Fig.  51. 
Skin,  H.  B.,  139-143. 
Skull,  H.  B.,  146,  Fig.  44. 
Sleep,  importance  of,  H.  B.,  129,  151, 

160. 

Sleeping  sickness,  A.  B.,  174. 
Slip,  P.  B.,  106. 
Small  intestine,  H.  B.,  97. 

absorption,  in,  H.  B.,  100. 
Smallpox,  H.  B.,  40. 
Smuts,  P.  B.,  152-153,  Fig.  77. 
Snail,  A.  B.,  Fig.  133. 
Snake,  A.  B.,  Fig.  135. 
Soda  water,  H.  B.,  66. 
Soil,  P.  B.,  110-114. 

air  in,  P.  B.,  111. 

cultivation  of,  P.  B.,  113. 

heat,  relation  of  soil  to,  P.  B.,  112. 

moisture  of,  P.  B.,  111. 
Soil  fertility,  relation  of  bacteria  to, 

H.  B.,  20. 
Soil  water, 

absorption  of,  P.  B.,  41. 

transmission  of,  P.  B.,  42,  48,  58. 
Soluble  mineral  matters,  H.  B.,  95. 
Soothing  sirups,  H.  B.,  78. 
Sorus  of  fern,  P.  B.,  162,  Fig.  82. 
Soups,  prepartaion  of,  H.  B.,  53. 
Source  of  energy,  P.  B.,  66. 
Sow  bug,  A.  B.,  Fig.  115. 
Sparrow,  A.  B.,  80,  90,  Fig.  70. 
Species,  plant,  P.  B.,  161,  170. 
Spermary,  A.  B.,  70. 

of  crayfish,  A.  B.,  159. 

of  fern,  P.  B.,  163. 

of  fish,  A.  B.,  137. 


of  frog,  A.  B.,  114. 
Sperm  cell, 

of  bee,  A.  B.,  36. 
of  bird,  A.  B.,  70,  Fig.  53. 
of  butterfly,  A.  B.,  11. 
of  crayfish,  A.  B.,  159. 
of  fern,  P.  B.,  163. 
of  fish,  A.  B.,  137. 
of  frog,  A.  B.,  114. 
of  grasshopper,  A.  B.,  28. 
Sperm  nucleus,  P.  B.,  77,  Figs.  27,  28, 

29. 

Spinal  cord,  H.  B.,  155. 
Spiracles,  A.  B.,  26. 
Spirilla,  H.  B.,  Fig.  7. 
Spirillum  form  of  bacteria,  P.  B.,  Fig. 

71,  D. 

Spirogyra,  P.  B.,  167,  Fig.  85. 
Sponges,  A.  B.,  175,  Fig.  123. 
Spore  formation  of  bacteria,  H.  B., 

13,  Fig.  7. 
Spore  formation  in  bacteria,  P.  B., 

143,  Fig.  71,  D. 
Spore  cases,  of  mold,  P.  B.,  150. 

of  ferns,  P.  B.,  162,  Figs.  82,  83. 
Sprains,  H.  B.,  149. 
Spreading  board,  A.  B.,  2,  Fig.  3. 
Spore-producing  plants,  P.  B.,  161- 

170. 
Spores, 

of  mold,  P.  B.,  150. 
of  ferns,  P.  B.,  162,  Figs.  82,  83. 
Spur,  P.  B.,  80. 
Squash,  cross-pollination,  P.  B.,  86, 

Fig.  32. 

Squash  seedling,  P.  B.,  Fig.  45. 
Stamens,  P.  B.,  71,  72,  80,  88,  Fig.  24. 
Staminate  flowers,  P.  B.,  87,  Figs.  32, 

A,  33. 
Starch, 

composition  of,  P.  B.,  13,  15. 
digestion  of,  P.  B.,  36,  37  ;  H.  B., 

90,  98. 
manufacture  by  chlorophyll,  P.  B., 

23,  90,  98. 
manufacture  by  different  kinds  of 

leaves,  P.  B.,  22,  footnote, 
manufacture  in  sunlight,  P.  B.,  22. 
test  for,  P.  B.,  15. 


INDEX 


227 


Stegomyia  mosquito,  A.  B.,  50,  174 ; 

H.  B.,  42. 
Stems, 

changes  during  growth,  P.  B.,  51. 

functions  of,  P.  B.,  48-51. 

structure,  P.  B.,  45-48. 
Stewifrg,  H.  B.,  53. 
Stickers,  P.  B.,  93. 
Stigma,  P.  B.,  72,  73,  81,  88,  Fig.  25. 
Stimulants  and  narcotics,  H.  B.t  64- 

81,  104-105,  143,  161-162. 
Sting  ray,  A.  B.,  Fig.  94. 
Stipules,  P.  B.,  56. 
Stock,  P.  B.,  105. 
Stoma,  P.  B.,  58,  60,  61,  62,  Figs.  21, 

22. 
Stomach, 

of  bee,  A.  B.,  39,  Fig.  28. 

of  fish,  A.  B.,  130,  Fig.  98. 

of  frog,  A.  B.,  108,  110,  Fig.  80. 

of  man  A.  B.,  2,  93-97,  99,  Fig.  2. 
Stone  fruits,  P.  B.,  96. 
Storage  of  foods,  P.  B.,  61. 
Strawberry,  flower,  P.  B.,  Fig.  41. 

fruit,  P.  B.,  Fig.  42. 

plant,  P.  B.,  Fig.  48. 
Struggle  for  existence  among  plants, 

P.  B.,  114-119,  Fig.  53. 
Style,  P.  B.,  73,  81,  88. 
Stylonychia,  A.  B.,  Fig.  117. 
Sucking  tube,  A.  B.,  6,  10. 
Suffocation,  H.  B.,  135. 
Sugars  as  part  of  diet,  H.  B.,  62. 
Sugar  cane,  P.  B.,  127. 
Summer  residents,  A.  B.,  81. 
Sun,  as  source  of  energy,  P.  B.,  66. 
Sunlight,  necessary  for  starch  manu- 
facture, P.  B.,  22. 
Supers,  A.  B.,  34,  Fig.  23. 
Survival  of  the  fittest,   P.  B.,   118- 

119,  Figs.  53,  55. 
Swarming,  A.  B.,  41,  Fig.  30. 
Sweat  glands,  H.  B.,  140,  Fig.  43. 
Sweeping,  proper  methods  of,  H.  B., 

25-29,  Fig.  11. 

Sweet  potato,  P.  B.,  127,  Fig.  60. 
Swim  bladder,  A.  B.,  127. 
Swimmeret,  A.  B.,  153,  159. 
Swimming  birds,  A.  B.,  76,  Fig.  57. 


Tadpole,  A.  B.,  116,  Fig.  84. 
Tapeworm,  A.  B.,  Fig.  129. 
Tarsus, 

of  bee,  A.  B.,  33. 

of  grasshopper,  A.  B.,  24. 
Tea,  P.  B.,  129,  Fig.  62. 

effect  on  body,  H.  B.,  65. 

preparation  of,  H.  B.,  65. 

use  and  abuse  of,  H.  B.,  65. 
Teeth, 

of  fish,  A.  B.,  128. 

of  frog,  A.  B.,  104. 
'  of  man,  H.  B.,  85-89. 
Temperature, 

effect  on  growth  of  bacteria,  H.  B., 
17. 

of  soil,  P.  B.,  112. 

relation    of,    to    germination    and 

growth,  P.  B.,  109. 
Tendons,  H.  B.,  3. 
Tentacles,  A.  B.,  176. 
Tent  for   consumptives,   H.   B.,   33, 

Fig.  15. 

Terminal  bud,  P.  B.,  53. 
Tern,  A.  B.,  95,  Figs.  49,  76. 
Thigh  of  grasshopper,  A.  B.f  24. 
Thorax,  A.  B.,  6. 
Throat,  H.  B.,  92,  126,  Fig.  39. 
Thrush,  A.  B.,  79,  Fig.  68. 
Tibia, 

of  bee,  A.  B.,  33. 

of  grasshopper,  A.  B.,  24. 
Tight  clothing,  effect  on  respiration, 

H.  B.,  133,  Fig.  43. 
Tissues,  H.  B.,  3. 

definition,  H.  B.,  4,  9. 
Toad,  A.  B.,  116,  Fig.  87. 
Toadstools,  P.  B.,  151. 
Tobacco,  H.  B.,  75-78. 
Tokay  grape  fruit,  P.  B.,  90. 
Tomato  fruit,  P.  B.,  90. 
Tongue, 

of  bee,  A.  B.,  32,  Fig.  25. 

of   frog,    A.    B.,     104,     110,    Fig. 
79. 

of  man,  H.  B.,  85. 
Tonsillitis,  H.  B.,  134. 
Tonsils,  H.  B.,  134,  Fig.  27. 
Topics,  order  of,  H.  B.,  178-180. 


228 


INDEX 


Total  abstinence  and  life  insurance, 

H.  B.,  73. 
Toxins,  H.  B.,  29. 

of  diphtheria,  H.  B.,  34. 
Trachea, 

of  frog,  A.  B.,  101. 

of  grasshopper,  A.  B.,  26,  Fig.  17. 
Transfer  of  food  materials,  P.  B.,  50, 

62. 
Transformations  of  energy,  P.  B.,  65  ; 

H.  B.,  123. 
Treatment, 

of  cuts,  H.  B.,  29. 

of  diphtheria,  H.  B.,  35. 

of  pneumonia,  H.  B.,  34. 

of  tuberculosis,  H.  B.,  32. 
Tree,  P.  B.,  154,  Figs.  78,  79. 
Trichina,  A.  B.,  Fig.  130. 
Tubercles  of  lung  tissue,  H.  B.,  32. 
Tubercles  on  roots,  H.  B.,  21,  Fig.  9. 
Tuberculosis,  H.  B.,  30-34. 
Tubers,  P.  B.,  107. 
Tufted  fruits  or  seeds,  P.  B.,  92. 
Tumbler  garden,  P.  B.,  102. 
Tulip,  flower,  P.  B.,  70-72. 
Turkey,  A.  B.,  78. 
Turtle,  A.  B.,  185. 
Tussock  moth,  A.  B.,  14,  Fig.  11. 
Tympanum,  H.  B.,  166. 
Typhoid  fever  due  to  bacteria,  P.  B., 
145;    H.  B.,  36-38. 

Umbo,  A.  B.,  181. 

Upper  lip,  A.  B.,  23,  Fig.  18. 

Use  of  foods,  economy  in,  H.  B.,  59. 

Uses, 

of  food  substances,  H.  B.,  50. 

of  forests,  P.  B.,  132-137. 

of  plants,  P.  B.,  127-132. 
Uvula,  H.  B.,  92. 

Vaccination,  H.  B.,  40. 

Vacuum  cleaner,  use  of,  H.  B.,  26, 

Fig.  11.        . 
Valves, 

in  arteries,  H.  B.,  114. 

of  heart,  H.  B.,  112,  Fig.  34. 

of  mussel,  A.  B.,  181. 
Vane  of  feather,  A.  B.,  67,  Fig.  50. 


Variation  among  plants,  P.  B.,  114, 

Fig.  52. 

Variety,  plant,  P.  B.,  161,  170. 
Vegetable  crop  of  New  York  State, 

P.  B.,  122. 
Vegetable  foods,  composition  of,  H. 

B.,  Fig.  20. 

Vegetable  mold,  P.  B.,  111. 
Veins  of  leaf,  P.  B.,  55. 
Veins, 

of  fish,  A.  B.,  131. 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  109,  116,  Fig.  37. 
Ventilation,  H.  B.,  136-138. 
Ventral,  A.  B.,  6. 
Ventricle, 

of  fish,  A.  B.,  132,  Fig.  100. 

of  frog,  A.  B.,  111. 

of  man,  H.  B.,  110,  Fig.  33. 
Vermiform  appendix,  H.  B.,  98. 
Vertebrae,  A.  B.,  190;    H.  B.,  144. 
Vertebrates,  A.  B.,  63,  190,  194. 
Villi,  H.  B.,  100,  Fig.  32. 
Vinegar,  preparation  of,  P.  B.,  145. 
Vocal  cords,  H.  B.,  126. 
Voluntary  muscles,  H.  B.,  151. 
Von  Behring,  H.  B.,  35. 
Vorticella,  A.  B.,  Fig.  117. 

Wading  birds,  A.  B.,  77,  Fig.  61. 
Walking  sticks,  A.  B.,  31,  Fig.  21. 
Wall, 

of  cell,  P.  B.,  28,  29. 

of  ovary,  P.  B.,  72,  73. 
Warbler,  A.  B.,  Fig.  72. 
Warm  baths,  H.  B.,  141. 
Water, 

as  a  part  of  diet,  H.  B.,  103. 

composition  and  preparation,  P.  B., 
10. 

given  off  from  leaves,  P.  B.,  59. 

in  human  body,  H.  B.,  45. 

osmosis  of,  P.  B.,  33. 

test  for,  P.  B.,  20. 

uses  of,  H.  B.,  52. 
Water  supplies,  H.  B.,  38. 
Wax  glands,  H.  B.,  166. 
Webber,  Dr.  H.  J.,  P.  B.,  120-122. 
Web-footed  birds,  A.  B.,  76,  Fig.  57. 


INDEX 


229 


Weed  seeds  destroyed  by  birds,  A.  B., 

85. 

Whale,  A.  B.,  Fig.  136. 
Whale  oil  soap,  A.  B.,  61. 
Wheat,  P.  B.,  128. 

seedling,  P.  B.,  Fig.  46. 
White  corpuscles,  H.  B.,  7,  Fig.  5; 

devouring  bacteria,  H.  B.,  29,  43, 

Fig.  12. 
White  matter  of  nervous  system,  H. 

B.,  157. 

Window  box,  P.  B.,  102. 
Windpipe, 

of  frog,  A.  B.,  101. 

of  man,  H.  B.,  126,  Fig.  40. 
Wine,  P.  B.,  129,  148. 
Winged  fruits,  P.  B.,  91. 
Wings, 

of  bee,  A.  B.,  32. 

of  bird,  A.  B.,  65. 

of  butterfly,  A.  B.,  7. 

of  grasshopper,  A.  B.,  25. 


Winter  visitants,  A.  B.,  81. 
Wood,  P.  B.,  46. 
Wood-cells,  P.  B.,  43,  49,  63. 
Woodpecker,  A.  B.,  79,  90,  Fig.  66. 
Woody  bundles,  P.  B.,  47,  50,   Fig. 

15. 
Worker  bees,  A.  B.,  37,  Figs.  24-28. 

Yeast,  P.  B.,  146-149,  Fig.  74. 

buds,  P.  B.,  146. 

changes  caused  by,  P.  B.,  147. 

reproduction  of,  P.  B.,  146. 

uses  of,  P.  B.,  148. 
Yellow  fever,  A.  B.,  50,   174;  H.  B.f 

42. 
Yolk, 

of  fish,  A.  B.,  140,  Fig.  103. 

of  hen's  egg,  A.  B.,  71,  Figs.  52, 
55. 

Zoology,  definition,  P.  B.,  4. 
Zygospores  of  spirogyra,  P.   B.,  168. 


'HE  following  pages  contain  advertisements  of  a 
few  of  the  Macmillan  books  on  kindred  subjects 


Chemistry 


BY  WILLIAM  CONGER  MORGAN,   PH.D.   (YALE) 

Assistant  Professor  of  Chemistry  in  the  University  of  California,  and 

JAMES   A.   LYMAN,   PH.D.    (]OHNS  HOPKINS) 
Professor  of  Chemistry  in  Pomona  College 

Cloth         ismo         429  pages         $1.25  net 

A  Laboratory  Manual  in  Chemistry 

BY  THE  SAME  AUTHORS 
Cloth         I2mo         142  pages         $  .40  net 

Chemistry  and  Laboratory  Manual 

$1.40  net 

The  characteristic  feature  of  these  new  books  is  the  success  with 
which  the  facts  of  everyday  life  have  been  utilized  and  made  an  essen- 
tial part  of  chemical  science.  This  feature  has  been  most  enthusi- 
astically commended  by  teachers  who  have  used  the  books  in  the 
classroom. 

With  the  practical  application  of  principles  is  combined  scientific 
accuracy  and  completeness.  The  treatment  has  been  made  interesting 
without  any  sacrifice  of  thoroughness. 

The  half-tone  illustrations  are  both  attractive  and  significant. 

The  questions  following  each  chapter  serve  at  once  to  provoke 
thought  and  to  relate  the  science  of  chemistry  to  the  experiences  of 
common  life. 

The  laboratory  exercises  are  so  chosen  and  worked  out  as  to  com- 
bine with  the  study  of  the  fundamental  principles  of  the  science,  illus- 
trations of  its  bearing  upon  human  welfare.  Chemical  science  is 
humanized  throughout. 

THE    MACMILLAN  COMPANY 

Publishers  64-66  Fifth  Avenue  New  York 

BOSTON  CHICAGO  DALLAS  SAN  FRANCISCO 


A  Laboratory  Manual 

FOR 

Physical  and  Commercial  Geography 

BY  RALPH  S.  TARR,  PH.D. 

Late  Professor  of  Geology  and  Physical  Geography  in  Cornell  University,  and 

O.  D.  VON  ENGELN,  Pn.D. 

Assistant  Professor  of  Geology  in  Cornell  University 
In  Press 

The  need  of  a  simple,  workable  Laboratory  Manual  for  use 
in  connection  with  the  study  of  Physical  and  Commercial  Geog- 
raphy has  been  felt  for  a  long  time.  This  new  Manual  is  ex- 
pressly designed  to  meet  this  need.  The  exercises  are  so 
planned  as  to  require  a  minimum  amount  of  apparatus,  most  of 
which  is  very  simple  in  character.  There  is  sufficient  variety 
in  these  exercises  to  render  them  adaptable  to  different  parts  of 
the  country,  and  they  are  not  too  difficult  for  use  by  first-year 
high  school  students.  By  means  of  them  the  student  is  taught 
to  exercise  his  judgment  and  to  realize  more  fully  the  signifi- 
cance of  the  facts  considered  in  the  text. 

A  special  feature  of  the  Manual  is  the  convenient  form  in 
which  it  is  prepared ;  while  stimulating  thought  it  saves  time 
and  labor  for  both  teacher  and  pupil. 

The  Manual  is  accompanied  by  a  Teacher's  Guide. 


THE  MACMILLAN   COMPANY 

Publishers  64-66  Fifth  Avenue  New  York 

BOSTON  CHICAGO  DALLAS  SAN  FRANCISCO 


Elements  of  Physics 


BY  HENRY  CREW 

Professor  of  Physics,  Northwestern  University 

REVISED  BY 

FRANKLIN  T.  JONES 

Teacher  of  Physics,  University  School,  Cleveland,  Ohio 

Cloth    i2tno    xiv  +  435  pages    $1.10 

It  is  the  aim  of  this  book  to  furnish  in  teachable  form  material  for  a  fundamental 
course  in  Physics  which  shall  be  within  the  comprehension  of  the  pupil  in  the  sec- 
ondary school.  The  authors  design  to  show  that  Physics  is  the  science  of  every- 
day life  and  that  it  is  a  logical  and  orderly  study. 

The  problems  and  exercises  in  this  text  are  unique.  Instead  of  the  old-fashioned, 
nerve-racking  problem  based  on  impossible  and  impractical  contingencies,  the  ex- 
ercises in  the  new  Crew  and  Jones  are  first  of  all  sensible.  They  are  designed  to 
be  practical  illustrations  of  the  actual  working  out  of  the  principles  of  Physics  and 
to  be  altogether  within  the  bounds  of  the  .mathematical  information  with  which  the 
average  high  school  pupil  finds  himself  equipped.  The  diagrams  and  illustrations 
in  the  text  are  clear  and  helpful.  They  add  much  to  the  attractiveness  and  to  the 
effectiveness  of  the  subject  matter.  The  formulae  are  derived  in  as  simple  a  way 
as  is  consistent  with  scientific  accuracy.  Long  mathematical  derivations,  always 
incomprehensible  to  the  young  student  and  therefore  an  unnecessary  aggravation 
to  him,  are  avoided.  The  treatment  of  the  text  will  be  found  throughout  up  to 
date,  interesting,  and  sound. 

Laboratory  Problems  in  Physics 

BY  FRANKLIN  T.  JONES 

Teacher  of  Physics,  University  School,  Cleveland 

AND 

ROBERT  R.   TATNALL,  PH.D. 

Instructor  in  Physics  in  Northwestern  University,  formerly  Instructor  in  Physics  in 
the  Academy  of  the  Northwestern  University 

Cloth    I2mo    ix  +  8i  pages    $.50 

The  student's  Manual  built  to  accompany  the  new  Crew  and  Jones  "  Elements 
of  Physics  "  is  a  complete  laboratory  manual  adapted  to  the  use  of  secondary 
schools.  It  has  been  the  object  of  the  authors  to  reduce  to  a  minimum  the  ex- 
penditure of  teaching  energy.  The  apparatus  suggested  for  use  in  the  laboratory 
is  simple,  inexpensive,  easily  obtained,  and  easily  duplicated.  The  book  is 
supremely  practical. 

THE    MACMILLAN    COMPANY 

Publishers  64-66  Fifth  Avenue  New  York 


ELEMENTS  OF  AGRICULTURE 


By  G.  F.  WARREN 

Professor  of  Farm  Management  and  Farm  Crops,  New  York  State  College  of 
Agriculture,  at  Cornell  University 

Cloth,  i2mo.        434  pages.        $1.10  net 


Upon  the  appearance  of  this  volume,  Mr.  W.  J.  Spillman  of 
the  United  States  Department  of  Agriculture,  Washington,  D.  C., 
wrote  as  follows : 


"  I  wish  to  congratulate  you  upon  this  book.  It  is  a  type  of  book 
which  has  been  much  needed.  We  have  had  a  large  number  of 
good  books  recently  that  were  not  up  to  high  school  grade.  Dr. 
Warren's  book  will  evidently  make  an  excellent  text  for  high  school 
work  in  agriculture.  It  is  comprehensive  and  at  the  same  time  in- 
tensive, considering  the  scope  which  it  must  necessarily  cover.  The 
subjects  are  well  chosen  and  are  excellently  treated.  I  predict  great 
usefulness  for  this  book." 


This  prediction  has  been  confirmed  not  only  by  the  words  of 
hundreds  of  teachers  who  have  used  the  book  and  found  it  emi- 
nently satisfactory,  but  by  the  fact  that  it  is  now  used  in  more 
than  one  thousand  schools  and  the  number  is  rapidly  increasing. 


PUBLISHED    BY 

THE   MACM-ILLAN   COMPANY 

64-66  Fifth  Avenue.  New  York 


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